Only move setting the executable bit to the build method

src/test/groovy/sdkman/stubs/UnameStub.groovy

@@ -12,6 +12,7 @@ class UnameStub {
 
 		def file = new File(folder, "uname")
 		file.createNewFile()
+		file.write "#!/usr/bin/env bash\n"
 
 		new UnameStub(file: file)
 	}
@@ -33,7 +34,6 @@ class UnameStub {
 
 	void build() {
 		file << """
-			|#!/usr/bin/env bash
 			|if [[ "\$1" == '-m' ]]; then
 			|	echo "$machine"
 			|elif [[ "\$1" == '-s' ]]; then