Manually upgrade PyArrow to 2.0.0

This is to make Airflow works with the new PIP 20.3.2
diff --git a/constraints-3.6.txt b/constraints-3.6.txt
index bdfcad8..5c07d3c 100644
--- a/constraints-3.6.txt
+++ b/constraints-3.6.txt
@@ -296,7 +296,7 @@
 py4j==0.10.9
 py==1.9.0
 pyOpenSSL==19.1.0
-pyarrow==0.17.1
+pyarrow==2.0.0
 pyasn1-modules==0.2.8
 pyasn1==0.4.8
 pycodestyle==2.6.0
diff --git a/constraints-3.7.txt b/constraints-3.7.txt
index 3e21df8..28d9999 100644
--- a/constraints-3.7.txt
+++ b/constraints-3.7.txt
@@ -291,7 +291,7 @@
 py4j==0.10.9
 py==1.9.0
 pyOpenSSL==19.1.0
-pyarrow==0.17.1
+pyarrow==2.0.0
 pyasn1-modules==0.2.8
 pyasn1==0.4.8
 pycodestyle==2.6.0
diff --git a/constraints-3.8.txt b/constraints-3.8.txt
index 3e21df8..28d9999 100644
--- a/constraints-3.8.txt
+++ b/constraints-3.8.txt
@@ -291,7 +291,7 @@
 py4j==0.10.9
 py==1.9.0
 pyOpenSSL==19.1.0
-pyarrow==0.17.1
+pyarrow==2.0.0
 pyasn1-modules==0.2.8
 pyasn1==0.4.8
 pycodestyle==2.6.0