Re-add the Go step via go-global-update (#823)

* Re-add the Go step via go-global-update

go-global-update (https://github.com/Gelio/go-global-update) is a small
tool to update all executables installed in a user's GOBIN, effectively
providing a `go get -u all` replacement for Go 1.16+.

Since it appears that Go will not be receiving a built-in way to do this
in the near future, this could be a good option in the meantime.

* Skip silently if go-global-update is not present

src/steps/generic.rs

@@ -63,6 +63,19 @@ pub fn run_flutter_upgrade(run_type: RunType) -> Result<()> {
     run_type.execute(&flutter).arg("upgrade").check_run()
 }
 
+pub fn run_go(run_type: RunType) -> Result<()> {
+    let go = utils::require("go")?;
+    let gopath = run_type.execute(&go).args(&["env", "GOPATH"]).check_output()?;
+
+    let go_global_update = utils::require("go-global-update")
+        .unwrap_or_else(|_| PathBuf::from(gopath).join("bin/go-global-update"))
+        .require()?;
+
+    print_separator("Go");
+
+    run_type.execute(&go_global_update).check_run()
+}
+
 pub fn run_gem(base_dirs: &BaseDirs, run_type: RunType) -> Result<()> {
     let gem = utils::require("gem")?;
     base_dirs.home_dir().join(".gem").require()?;