Added go.mod file to go/cbrotli directory (#754)

* Added go.mod file

* go.mod removed go version
diff --git a/go/cbrotli/go.mod b/go/cbrotli/go.mod
new file mode 100644
index 0000000..cd8c859
--- /dev/null
+++ b/go/cbrotli/go.mod
@@ -0,0 +1 @@
+module github.com/google/brotli/go/cbrotli