chore: fix comment typo

src/core/instance/lifecycle.js

@@ -193,7 +193,7 @@ export function mountComponent (
     }
   }
 
-  // we set this to vm._watcher inside the wathcer's constructor
+  // we set this to vm._watcher inside the watcher's constructor
   // since the watcher's initial patch may call $forceUpdate (e.g. inside child
   // component's mounted hook), which relies on vm._watcher being already defined
   new Watcher(vm, updateComponent, noop, null, true /* isRenderWatcher */)