Fixed copy handlers script. (#7)

Author: GiedriusGrabauskas

package.json

@@ -16,7 +16,7 @@
     "postbuild": "uglifyjs ./dist/simplr-logger.js -o ./dist/simplr-logger.min.js --compress --mangle",
     "build-handlers": "webpack --config webpack.handlers-config.js",
     "postbuild-handlers": "uglifyjs ./dist/simplr-logger-handlers.js -o ./dist/simplr-logger-handlers.min.js --compress --mangle",
-    "precopy-handlers": "rimraf ./handlers.js && rimraf ./handlers.d.ts",
+    "precopy-handlers": "rimraf ./handlers.js && rimraf ./handlers.d.ts && cd scripts/copy-handlers && npm i",
     "copy-handlers": "rimraf @types && tsc -p . --outDir _dist_temp && cd scripts/copy-handlers && npm run copy",
     "watch": "webpack --watch",
     "prerelease": "npm run clear",