Added jarRepositories.xml as an optional ignore (#3254)

Since IntelliJ 2019.3 this file appeared in our git changes. It seems these are just cached information about remote repositories that are defined in Maven/Gradle.

Global/JetBrains.gitignore

@@ -30,6 +30,7 @@
 # auto-import.
 # .idea/artifacts
 # .idea/compiler.xml
+# .idea/jarRepositories.xml
 # .idea/modules.xml
 # .idea/*.iml
 # .idea/modules