Fix double slash links (#5049)

Summary:
Expanding upon #5039 to catch all such instances.

Search for regex `\.mdx?/`.

Pull Request resolved: #5049

Test Plan: Ran the docs in dev mode and confirmed that I could click the link and get to the why-null page at the right anchor

Reviewed By: evanyeung

Differential Revision: D79477408

Pulled By: captbaritone

fbshipit-source-id: 1d2ce71714ba7d7309029081288cbb8e342f510d

Author: captbaritone

website/docs/guides/throw-on-field-error-directive.md

@@ -15,7 +15,7 @@ The `@throwOnFieldError` directive can be added to fragments and queries. When
 this directive is used, the Relay runtime will throw an exception if a field
 with a field error is encountered while reading the fragment or query, or if
 Relay is missing data due to a
-[graph relationship change](../debugging/why-null.md/#graph-relationship-change).
+[graph relationship change](../debugging/why-null.md#graph-relationship-change).
 
 In addition to causing the Relay runtime to throw an exception if a field error
 is encountered, the `@throwOnFieldError` directive also enables generation of

website/versioned_docs/version-v18.0.0/guides/throw-on-field-error-directive.md

@@ -15,7 +15,7 @@ The `@throwOnFieldError` directive can be added to fragments and queries. When
 this directive is used, the Relay runtime will throw an exception if a field
 with a field error is encountered while reading the fragment or query, or if
 Relay is missing data due to a
-[graph relationship change](../debugging/why-null.md/#graph-relationship-change).
+[graph relationship change](../debugging/why-null.md#graph-relationship-change).
 
 In addition to causing the Relay runtime to throw an exception if a field error
 is encountered, the `@throwOnFieldError` directive also enables generation of

website/versioned_docs/version-v19.0.0/guides/throw-on-field-error-directive.md

@@ -15,7 +15,7 @@ The `@throwOnFieldError` directive can be added to fragments and queries. When
 this directive is used, the Relay runtime will throw an exception if a field
 with a field error is encountered while reading the fragment or query, or if
 Relay is missing data due to a
-[graph relationship change](../debugging/why-null.md/#graph-relationship-change).
+[graph relationship change](../debugging/why-null.md#graph-relationship-change).
 
 In addition to causing the Relay runtime to throw an exception if a field error
 is encountered, the `@throwOnFieldError` directive also enables generation of

website/versioned_docs/version-v20.0.0/guides/throw-on-field-error-directive.md

@@ -15,7 +15,7 @@ The `@throwOnFieldError` directive can be added to fragments and queries. When
 this directive is used, the Relay runtime will throw an exception if a field
 with a field error is encountered while reading the fragment or query, or if
 Relay is missing data due to a
-[graph relationship change](../debugging/why-null.md/#graph-relationship-change).
+[graph relationship change](../debugging/why-null.md#graph-relationship-change).
 
 In addition to causing the Relay runtime to throw an exception if a field error
 is encountered, the `@throwOnFieldError` directive also enables generation of

website/versioned_docs/version-v20.1.0/guides/throw-on-field-error-directive.md

@@ -15,7 +15,7 @@ The `@throwOnFieldError` directive can be added to fragments and queries. When
 this directive is used, the Relay runtime will throw an exception if a field
 with a field error is encountered while reading the fragment or query, or if
 Relay is missing data due to a
-[graph relationship change](../debugging/why-null.md/#graph-relationship-change).
+[graph relationship change](../debugging/why-null.md#graph-relationship-change).
 
 In addition to causing the Relay runtime to throw an exception if a field error
 is encountered, the `@throwOnFieldError` directive also enables generation of