Fix source maps generation

Enabling the `sourceMap` option always crashed the plugin for me. So I went through the code and noticed that `inputSourceMap` should be passed to the `transfer` function from `multi-stage-sourcemap` instead of `inputSource`

Author: praneetrohida

index.ts

@@ -42,7 +42,7 @@ class WebpackObfuscator {
                     if (this.options.sourceMap && inputSourceMap) {
                         const transferredSourceMap = transferSourceMap({
                             fromSourceMap: obfuscationSourceMap,
-                            toSourceMap: inputSource
+                            toSourceMap: inputSourceMap
                         });
 
                         compilation.assets[fileName] = new SourceMapSource(
@@ -89,4 +89,4 @@ class WebpackObfuscator {
     }
 }
 
-export = WebpackObfuscator;
+export = WebpackObfuscator;