Fix travis mac builds stability

[valich]

Gradle tasks fail on mac travis with ~50% probability due to some VM misconfiguration. In the log it appears as

:ide-plugin:testJava HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=250m; support was removed in 8.0
Error occurred during initialization of VM
java/lang/NoClassDefFoundError: java/lang/Object
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=250m; support was removed in 8.0
WARNING: GL pipe is running in software mode (Renderer ID=0x1020400)
:ide-plugin:test FAILED
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

Strangely, compilation is fine so maybe it's Kotlin interop problem.

[valich]

Mac builds disabled until better times (moving to other CI or travis fixing mac builds)