Update contribute/backend/style-guide.md

Co-authored-by: Jack Baldry <[email protected]>

contribute/backend/style-guide.md

@@ -66,7 +66,7 @@ Use [`t.Cleanup`](https://golang.org/pkg/testing/#T.Cleanup) to clean up resourc
 
 ### Mock
 
-Optionally, we use [`mock.Mock`](https://github.com/stretchr/testify#mock-package) package to write mocks. 
+Optionally, we use [`mock.Mock`](https://github.com/stretchr/testify#mock-package) package to write mocks.
 This is useful when you expect different behaviors of the same function.
 
 #### Tips