Suppress build error

This build error doesn't appear locally and I can't reproduce it, but
I've heard others report it, and now Travis is having it as an issue.

I'm going to try to explicitly specify this dependency to see if it
makes a difference.

package.json

@@ -25,7 +25,8 @@
     "@babel/preset-env": "^7.3.1",
     "@babel/preset-typescript": "^7.3.3",
     "google-auth-library": "^3.1.0",
-    "image-size": "^0.7.2"
+    "image-size": "^0.7.2",
+    "output-file-sync": "^2.0.1"
   },
   "devDependencies": {
     "@types/jquery": "^3.3.29",
@@ -34,7 +35,7 @@
     "mocha": "^6.0.2",
     "preact": "^8.3.1",
     "tslint": "^5.13.0",
-    "typescript": "^3.7.0-dev.20191011"
+    "typescript": "^3.7.0"
   },
   "private": true
 }