src: fix typo rval to value

rval never existed, it was added as that in 077f9d7

Fixes: nodejs#9001

src/node.cc

@@ -2711,7 +2711,7 @@ static void EnvSetter(Local<String> property,
     SetEnvironmentVariableW(key_ptr, reinterpret_cast<WCHAR*>(*val));
   }
 #endif
-  // Whether it worked or not, always return rval.
+  // Whether it worked or not, always return value.
   info.GetReturnValue().Set(value);
 }