Add tslib@^2.0.0 dependency

Error on createExtension coc-phpactor from ~/.config/coc/extensions/node_modules/coc-phpactor/lib/extension.js Error: Cannot find module 'tslib'.

Author: premyslruzicka

package.json

@@ -58,5 +58,6 @@
         "webpack-cli": "^3.3.4"
     },
     "dependencies": {
+        "tslib": "^2.0.0"
     }
 }