chore(deps): update dependency pyarrow to v6 (#37)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [pyarrow](https://arrow.apache.org/) | ` >= 3.0.0, < 6.0dev` -> `>=3.0.0, <6.1` | [![age](https://badges.renovateapi.com/packages/pypi/pyarrow/6.0.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/pyarrow/6.0.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/pyarrow/6.0.0/compatibility-slim/5.0.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/pyarrow/6.0.0/confidence-slim/5.0.0)](https://docs.renovatebot.com/merge-confidence/) |

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setup.py

@@ -31,7 +31,7 @@
 dependencies = [
     "packaging >= 17.0",
     "pandas >= 0.24.2, < 2.0dev",
-    "pyarrow >= 3.0.0, < 6.0dev",
+    "pyarrow>=3.0.0, <7.0dev",
     "numpy >= 1.16.6, < 2.0dev",
 ]