Update kotlin version to 1.6.10 (#266)

Summary:
Running `mvn install` on macOS with JDK15 results in illegal access
exceptions. This appears to be a known issue that was fixed in 1.5.30:
https://youtrack.jetbrains.com/issue/KT-45689

It would be a nice quality of life improvement to bump the kotlin
version if this doesn't conflict with any internal flows.

Pull Request resolved: #266

Reviewed By: hick209

Differential Revision: D33338988

Pulled By: cgrushko

fbshipit-source-id: 4eaef0c9dd44b35d2c9556bf176a44a3b52a2db7

core/pom.xml

@@ -16,7 +16,7 @@
 
  <properties>
  <dokka.version>0.10.1</dokka.version>
- <kotlin.version>1.5.0</kotlin.version>
+ <kotlin.version>1.6.10</kotlin.version>
  <kotlin.compiler.incremental>true</kotlin.compiler.incremental>
  <kotlin.compiler.jvmTarget>1.8</kotlin.compiler.jvmTarget>
  <main.class>com.facebook.ktfmt.cli.Main</main.class>