Move mocha to a dependency since it's is actually a dep not a devDep in this case

contracts/test-utils/package.json

@@ -35,7 +35,6 @@
     "homepage": "https://github.com/0xProject/0x-monorepo/contracts/test-utils/README.md",
     "devDependencies": {
         "@types/mocha": "^5.2.7",
-        "mocha": "^6.2.0",
         "npm-run-all": "^4.1.2",
         "shx": "^0.2.2",
         "tslint": "5.11.0",
@@ -68,7 +67,8 @@
         "ethers": "~4.0.4",
         "js-combinatorics": "^0.5.3",
         "lodash": "^4.17.11",
-        "make-promises-safe": "^1.1.0"
+        "make-promises-safe": "^1.1.0",
+        "mocha": "^6.2.0"
     },
     "publishConfig": {
         "access": "public"