Add gypcmd extension wildcard to git ignore.

These files are generated by the msvs-ninja gyp generator.

BUG=481707

Review URL: https://codereview.chromium.org/1134493004

Cr-Commit-Position: refs/heads/master@{#330618}

.gitignore

+*.gypcmd
 *.mk
 *.ncb
 *.opensdf