Add build for python 3.7 on linux and windows

kokoro/release/python/linux/build_artifacts.sh

@@ -43,6 +43,7 @@ build_artifact_version 2.7
 build_artifact_version 3.4
 build_artifact_version 3.5
 build_artifact_version 3.6
+build_artifact_version 3.7
 
 # Build source package
 

kokoro/release/python/windows/build_artifacts.bat

@@ -51,3 +51,13 @@ SET PYTHON=C:\python36
 SET PYTHON_VERSION=3.6
 SET PYTHON_ARCH=64
 CALL build_single_artifact.bat
+
+SET PYTHON=C:\python37_32bit
+SET PYTHON_VERSION=3.7
+SET PYTHON_ARCH=32
+CALL build_single_artifact.bat
+
+SET PYTHON=C:\python37
+SET PYTHON_VERSION=3.7
+SET PYTHON_ARCH=64
+CALL build_single_artifact.bat