Update version to 1.15.1 to be in sync with pip version and tags

tensorflow_estimator/tools/pip_package/setup.py

@@ -30,7 +30,7 @@
 # This version string is semver compatible, but incompatible with pip.
 # For pip, we will remove all '-' characters from this string, and use the
 # result for pip.
-_VERSION = '1.15.0'
+_VERSION = '1.15.1'
 
 REQUIRED_PACKAGES = [
  # We depend on TensorFlow's declared pip dependencies.