Remove extra semi colon from fatal/string/rope.h

Summary:
`-Wextra-semi` or `-Wextra-semi-stmt`

If the code compiles, this is safe to land.

Reviewed By: dmm-fb

Differential Revision: D52965935

fbshipit-source-id: ff098f6836e0175b4f8be41874890147e8195d24

fatal/string/rope.h

@@ -1172,7 +1172,7 @@ struct rope {
       } else {
         break;
       }
-    };
+    }
 
     return begin;
   }
@@ -1500,7 +1500,7 @@ struct rope {
         auto const off = static_cast<size_type>(std::distance(ref.begin(), j));
         return const_iterator(this, std::addressof(pieces_[i]), i, off);
       }
-    };
+    }
 
     return cend();
   }