Disable source maps for node_modules (facebook#5096)

Author: Timer

packages/react-scripts/config/webpack.config.dev.js

@@ -308,6 +308,11 @@ module.exports = {
                   ]),
                   // @remove-on-eject-end
                   highlightCode: true,
+                  // If an error happens in a package, it's possible to be
+                  // because it was compiled. Thus, we don't want the browser
+                  // debugger to show the original code. Instead, the code
+                  // being evaluated would be much more helpful.
+                  sourceMaps: false,
                 },
               },
             ],

packages/react-scripts/config/webpack.config.prod.js

@@ -342,6 +342,11 @@ module.exports = {
                   ]),
                   // @remove-on-eject-end
                   highlightCode: true,
+                  // If an error happens in a package, it's possible to be
+                  // because it was compiled. Thus, we don't want the browser
+                  // debugger to show the original code. Instead, the code
+                  // being evaluated would be much more helpful.
+                  sourceMaps: false,
                 },
               },
             ],