Buck: Strip SNAPSHOT suffix in artifact names only for GERRIT repositories

Maven artifact names on Google bucket replacing SNAPSHOT suffix with
timestamp. 731967591ef98ab3c94691ba9dc0f217630dda76 changed this by
preserving the SNAPSHOT suffix. This broke fetching of gwtorm and
gwtjsonrpc and was reverted by 731967591ef98ab3c94691ba9dc0f217630dda76.

This change fixes this for both worlds: stripping it for GERRIT and
GERRIT_API Maven repositories but preserving it for the rest.

Test plan:

maven_jar() is working as expected for the both worlds:

* gwtorm:gwtorm:1.10-SNAPSHOT-20140310.015132-1 (repo = GERRIT)
* org.eclipse.jgit:org.eclipse.jgit:3.4.0-SNAPSHOT (repo = MAVEN_LOCAL)

Change-Id: I5357abe9ad6a40538c444ad70016c8c6d75d8ff3
diff --git a/lib/maven.defs b/lib/maven.defs
index 9eed538..0ac5005 100644
--- a/lib/maven.defs
+++ b/lib/maven.defs
@@ -48,7 +48,7 @@
     raise NameError('expected id="groupId:artifactId:version"')
   group, artifact, version = parts
 
-  if 'SNAPSHOT' in version:
+  if 'SNAPSHOT' in version and repository.startswith(GERRIT):
     file_version = version.replace('-SNAPSHOT', '')
     version = version.split('-SNAPSHOT')[0] + '-SNAPSHOT'
   else: