chore(release): workaround npm issue where .git/ dir is published

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

npm publish publishes the .git/ directory in our release directory (./bower-material/) during the release process.

Issue Number:
Fixes #11684

What is the new behavior?

The ./bower-material/.git/ directory is removed before doing npm publish.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This needs to be merged before the next release (1.1.18).

[jelbourn]

LGTM