The config name is sourceMaps not sourceMap (#3588)

packages/babel-register/src/node.js

@@ -69,7 +69,7 @@ function compile(filename) {
       // Do not process config files since has already been done with the OptionManager
       // calls above and would introduce duplicates.
       babelrc: false,
-      sourceMap: "both",
+      sourceMaps: "both",
       ast:       false
     }));
   }