Fix publish-android-snapshot issues

Summary:
As expected, this didn't work on the first try. Issues I've fixed:

- Actually switch back to snapshots.
- Use more widely compatible bash location.
- Don't exit (because of `set -e`) if `grep` returns with status 1.

Reviewed By: jknoxville

Differential Revision: D9556770

fbshipit-source-id: 0900e6498e7fc8e16c941e77927005573ca310d5

gradle.properties

@@ -1,5 +1,5 @@
 # POM publishing constants
-VERSION_NAME=0.6.18
+VERSION_NAME=0.6.19-SNAPSHOT
 GROUP=com.facebook.flipper
 POM_URL=https://github.com/facebook/flipper
 POM_SCM_URL=https://github.com/facebook/flipper.git