increase compile.zinc integration test timeout

This target is consistently hitting the 60-second default timeout on my and Peiyu's laptops (I also tried rebooting).
We're getting 130-180 seconds when running with --no-test-pytest-timeouts.

Testing Done:
ran tests locally, didn't time out

https://travis-ci.org/pantsbuild/pants/builds/112191835

Bugs closed: 2976

Reviewed at https://rbcommons.com/s/twitter/r/3507/

tests/python/pants_test/backend/jvm/tasks/jvm_compile/zinc/BUILD

@@ -8,6 +8,7 @@ python_tests(
   dependencies=[
     'tests/python/pants_test/backend/jvm/tasks/jvm_compile:base_compile_integration_test',
   ],
+  timeout = 300,
   tags = {'integration'},
 )