Make bignumber.js types normal dependency

package.json

@@ -51,7 +51,6 @@
     "node": ">=6.0.0"
   },
   "devDependencies": {
-    "@types/bignumber.js": "^4.0.2",
     "@types/jsonschema": "^1.1.1",
     "@types/lodash": "^4.14.64",
     "@types/mocha": "^2.2.41",
@@ -90,6 +89,7 @@
     "webpack": "^3.1.0"
   },
   "dependencies": {
+    "@types/bignumber.js": "^4.0.2",
     "0x-json-schemas": "^0.5.1",
     "bignumber.js": "^4.0.2",
     "compare-versions": "^3.0.1",