remove code not needed from npmAddScriptSync.js

(lib/utils/npmAddScriptSync.js)

discovered thanks to mutation testing using Stryker

Author: Christopher J. Brody

lib/utils/npmAddScriptSync.js

@@ -7,9 +7,6 @@ module.exports = (packageJsonPath, script, fs) => {
   try {
     var packageJson = jsonfile.readFileSync(packageJsonPath, { fs });
     if (!packageJson.scripts) packageJson.scripts = {};
-    if (!script.force && packageJson.scripts[script.key]) {
-      throw new Error(`That script entry for key: ${script.key} already exists.`);
-    }
     packageJson.scripts[script.key] = script.value;
     jsonfile.writeFileSync(packageJsonPath, packageJson, { fs, spaces: 2 });
   } catch (e) {