fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321969
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321970

requirements.txt

@@ -66,7 +66,7 @@ monotonic==1.5            # via fasteners
 mox==0.5.3                # via googleappenginemapreduce
 msgpack==1.0.2            # via cachecontrol
 mutagen==1.43.0           # via -r requirements.in
-numpy==1.16.6             # via apache-beam, pyarrow
+numpy==1.22.0rc1             # via apache-beam, pyarrow
 oauth2client==3.0.0       # via apache-beam, google-apitools
 packaging==20.4           # via -r requirements.in, bleach
 pbr==5.5.1                # via mock