Bump pyarrow from 3.0.0 to 4.0.0

Bumps [pyarrow](https://arrow.apache.org/) from 3.0.0 to 4.0.0.

requirements.txt

@@ -6,8 +6,8 @@ mlxtend==0.18.0
 numba==0.53.1
 numpy==1.20.2
 outlier-utils==0.0.3
+pyarrow==4.0.0
 pandas==1.2.4
-pyarrow==3.0.0
 pytest==6.2.3
 pytest-lazy-fixture==0.6.3
 PyWavelets==1.1.1