cmd/gomobile: fix minSdkVersion formatting for bind.
cmd/gomobile: fix minSdkVersion formatting for bind.

The fix for golang/go#12661 was incorrect.

Fixes golang/go#12809.

Change-Id: Ic2cfedcc99ced0241a5756fb36f6f9ae5a6b7287
Reviewed-on: https://go-review.googlesource.com/15270
Reviewed-by: Burcu Dogan <347c19a639ce752a783b4ea325d6539ab4b4a262@google.com>

golang/mobile,golang/mobile,golang/mobile,golang/mobile