prevent source map in demo builds

Author: liabru

.gitignore

@@ -1,4 +1,5 @@
 .idea
+*.map
 node_modules
 npm-debug.log
 docs
@@ -15,4 +16,4 @@ test/browser/refs
 test/node/diffs
 test/node/refs
 __snapshots__
-__compare__
+__compare__

webpack.demo.config.js

@@ -29,7 +29,7 @@ License ${pkg.license}`;
     return {
         entry: { [name]: './demo/src/index.js' },
         node: false,
-        devtool: 'source-map',
+        devtool: devServer ? 'source-map' : 'none',
         output: {
             library: 'MatterDemo',
             libraryTarget: 'umd',