Handle versions of the form -a.b.c+foo.

Previously we would keep the +x.y.z part, which caused errors in Soong.

See the diff between the first two patchsets in aosp/1833319 for an
example.

Test: Fix the above CL and run on a crate without a +.
Change-Id: I791c85545e67b54e2c8952428211688e7bbf580d
1 file changed