build: add husky ignored files to .gitignore

Ahead of upgrading to husky v5, adding the shell file location
to .gitignore to prevent it from randomly showing up when devs
checkout older branches.

(cherry picked from commit c24008c)

Author: josephperrott

.gitignore

@@ -42,6 +42,7 @@ yarn-error.log*
 .ng_pkg_build/
 .ng-dev.log
 .ng-dev.user*
+.husky/_
 
 # Mac OSX Finder files.
 **/.DS_Store