docs: refactor codebase and update documentation

- Update installation command from `go get` to `go install` in README.md

Signed-off-by: appleboy <appleboy.tw@gmail.com>

README.md

@@ -37,7 +37,7 @@ The pre-compiled binaries can be downloaded from [release page](https://github.c
 With `Go` installed
 
 ```sh
-go get -u -v github.com/appleboy/drone-jenkins
+go install github.com/appleboy/drone-jenkins
 ```
 
 or build the binary with the following command: