chore: pin versions of dependencies for compatibility with Python 3.6 (#1588) (#2144)
chore: pin versions of dependencies for compatibility with Python 3.6 (#1588) (#2144)

* chore: pin versions of dependencies for compatibility with Python 3.6

* fix path of requirements file in synthtool
Source-Link: https://github.com/googleapis/synthtool/commit/69cdb47824170d0b02bf694649ce66613c889040
Post-Processor: 48d5800083e04fbe06b7d85b0e411aebd73b5710@sha256:6566dc8226f20993af18e5a4e7a2b1ba85a292b02dedb6a1634cf10e1b418fa5
googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client