Remove double spaces after dots in comments

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -438,7 +438,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUn
             // when this coercion occurs, we would be changing the
             // field `ptr` from a thin pointer of type `*mut [i32;
             // 3]` to a fat pointer of type `*mut [i32]` (with
-            // extra data `3`).  **The purpose of this check is to
+            // extra data `3`). **The purpose of this check is to
             // make sure that we know how to do this conversion.**
             //
             // To check if this impl is legal, we would walk down