fix: remove trailing newline in build.go

Fixed formatting issue that was causing CI to fail.
The file had an extra blank line at the end which go fmt removed.

🤖 Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <luoliwoshang@users.noreply.github.com>

runtime/internal/lib/go/build/build.go

@@ -135,4 +135,3 @@ func defaultGOPATH() string {
 	}
 	return ""
 }
-