Relax bundler dep until 1.3.0 is actually released.

Revert "Bump bundler dep to 1.3.0.pre.4+ to introduce 'bundle binstubs <gem>'"

This reverts commit e00b8ecf1ad8984b760f12e61247820613aec4ee.

Revert "Use bundler --pre for travis builds"

This reverts commit 4d240ec20a70122b7e69c790a37d2be14e1ff038.