Bump httplib2 from 0.9.2 to 0.18.0 in /build (#1272)

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.9.2 to 0.18.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](https://github.com/httplib2/httplib2/compare/0.9.2...v0.18.0)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build/requirements.txt

@@ -1,2 +1,2 @@
 flake8>=3.5.0
-httplib2==0.9.2
+httplib2==0.18.0