fix(package): remove install script

The package is built before publish. End users can rebuild if desired.

package.json

@@ -11,7 +11,6 @@
   "scripts": {
     "build": "gulp && npm run clean-build",
     "clean-build": "trash dist/plugin.min.js && trash dist/www.min.js && trash src/browser/worker.min.js",
-    "install": "npm run build",
     "test": "npm run jshint",
     "jshint": "jshint src/browser/src && jshint src/common/src && jshint tests",
     "gen-tests": "npm run build && npm run clean-platform-tests && npm run mkdirp-platform-tests && npm run copy-platform-tests && npm run install-platform-tests",
@@ -24,7 +23,7 @@
     "test:browser": "cd ../cordova-plugin-test-projects/cordova-plugin-qrscanner-tests && npm run test:browser",
     "test:library": "npm run build && node tests/library/test.js",
     "changelog": "conventional-changelog -p angular -i CHANGELOG.md -s",
-    "prep-release": "git clean -dfx && npm install && npm run changelog"
+    "prep-release": "git clean -dfx && npm run build && npm run changelog"
   },
   "repository": {
     "type": "git",