fix: clean dist before building

Author: davewasmer

package.json

@@ -31,7 +31,7 @@
     "typescript": "2.2.0"
   },
   "scripts": {
-    "build": "tsc && mv dist/bin/denali.js dist/bin/denali && chmod +x dist/bin/denali && echo 'Build successful'",
+    "build": "rm -r dist && tsc && mv dist/bin/denali.js dist/bin/denali && chmod +x dist/bin/denali && echo 'Build successful'",
     "prepublish": "in-publish && npm run build || not-in-publish",
     "lint": "! tslint --project tsconfig.json -c tslint.json --type-check | sed \"s|$PWD/||\" | grep ERROR",
     "test": "npm run lint && rm -rf dist coverage .nyc_output && npm run build && nyc ava dist/test/acceptance"