Update project.clj with proper case for dependency

[jw2249a]

Error reads: Could not start nREPL server: Could not find artifact org.clojure:clojure:jar:1.9.0-rc2 in central (https://repo1.maven.org/maven2/)
Could not find artifact org.clojure:clojure:jar:1.9.0-rc2 in clojars (https://repo.clojars.org/)

location is :dependencies [[org.clojure/clojure "1.9.0-RC2"]

Fixed case to RC2 and it worked fine https://repo1.maven.org/maven2/org/clojure/clojure/1.9.0-RC2/