Pin dependencies (googleworkspace#297)

Co-authored-by: renovate[bot] <renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package.json

@@ -14,23 +14,23 @@
   },
   "homepage": "https://github.com/googlesamples/apps-script-oauth2",
   "devDependencies": {
-    "@google/clasp": "^2.3.0",
-    "chai": "^4.2.0",
-    "del": "^1.2.1",
-    "eslint": "^4.19.1",
-    "eslint-config-google": "^0.9.1",
-    "fibers": "^4.0.2",
-    "gas-local": "^1.3.1",
-    "gulp": "^4.0.2",
-    "gulp-clean": "^0.4.0",
-    "gulp-concat": "^2.6.1",
-    "gulp-contains": "^1.2.0",
-    "gulp-eslint": "^4.0.2",
+    "@google/clasp": "2.3.1",
+    "chai": "4.2.0",
+    "del": "1.2.1",
+    "eslint": "4.19.1",
+    "eslint-config-google": "0.9.1",
+    "fibers": "4.0.2",
+    "gas-local": "1.3.1",
+    "gulp": "4.0.2",
+    "gulp-clean": "0.4.0",
+    "gulp-concat": "2.6.1",
+    "gulp-contains": "1.2.0",
+    "gulp-eslint": "4.0.2",
     "gulp-expose": "0.0.7",
-    "gulp-rename": "^1.4.0",
-    "jsdoc": "^3.6.4",
-    "mocha": "^5.0.0",
-    "urlsafe-base64": "^1.0.0"
+    "gulp-rename": "1.4.0",
+    "jsdoc": "3.6.4",
+    "mocha": "5.0.3",
+    "urlsafe-base64": "1.0.0"
   },
   "scripts": {
     "preversion": "npm test && cd src/ && clasp push",