docs(readme): hyphenate first-class

Author: dackers86

README.md

@@ -27,7 +27,7 @@ React Native Firebase is built with four key principles in mind;
 - 🧪 **Well tested**
   - every module is extensively tested to >95% coverage
 - 👁 **Well typed**
-  - first class support for TypeScript included
+  - first-class support for TypeScript included
 - 📄 **Well documented**
   - full reference & installation documentation alongside detailed guides and FAQs
 - 🔥 **Mirrors official Firebase Web SDK**