Update src/implementing_new_feature.md

Co-Authored-By: rajcspsg <[email protected]>

Author: mark-i-m

src/implementing_new_feature.md

@@ -115,7 +115,7 @@ The current version is not actually important – the important version is when
 
     You can check it in most places in the compiler using the expression `tcx.features().$feature_name` (or `sess.features_untracked().borrow().$feature_name` if the tcx is unavailable)
 
-If the feature gate is not set, you should either maintain the pre-feature behavior or raise an error, depending on what makes sense.
+    If the feature gate is not set, you should either maintain the pre-feature behavior or raise an error, depending on what makes sense.
 
 5. Add a test to ensure the feature cannot be used without a feature gate, by creating `feature-gate-$feature_name.rs` and `feature-gate-$feature_name.stderr` files under the `src/test/ui/feature-gates` directory.