chore(deps): pin dependencies

package.json

@@ -29,15 +29,15 @@
     "word-wrap": "^1.0.3"
   },
   "devDependencies": {
-    "@types/chai": "^4.1.7",
-    "@types/mocha": "^5.2.7",
-    "chai": "^4.2.0",
-    "cosmiconfig": "^5.2.1",
-    "mocha": "^6.2.0",
-    "mock-require": "^3.0.3",
-    "prettier": "^1.15.3",
+    "@types/chai": "4.1.7",
+    "@types/mocha": "5.2.7",
+    "chai": "4.2.0",
+    "cosmiconfig": "5.2.1",
+    "mocha": "6.2.0",
+    "mock-require": "3.0.3",
+    "prettier": "1.15.3",
     "semantic-release": "^15.13.3",
-    "semver": "^6.2.0"
+    "semver": "6.2.0"
   },
   "optionalDependencies": {
     "@commitlint/load": ">6.1.1"