Update version to 0.8.1 (#667)

Author: longquanzheng

internal/version.go

@@ -35,7 +35,7 @@ package internal
 // that are writing workflows. So every time we change API
 // that can affect them we have to change this number.
 // Format: MAJOR.MINOR.PATCH
-const LibraryVersion = "0.7.0"
+const LibraryVersion = "0.8.1"
 
 // FeatureVersion is a semver that represents the
 // feature set of this cadence client library support.