Add a clean target
This change just adds a clean target to the MuJS compiler's package
file.  If you rename tests, the old files stick around inside of bin/,
possibly causing superfluous test failures.  A clean does the trick.
"main": "bin/lib/index.js",
"typings": "bin/lib/index.d.ts",
"scripts": {
+ "clean": "rm -rf bin/",
"build": "tsc && tslint 'cmd/**/*.ts' 'lib/**/*.ts' 'tests/**/*.ts' && npm run copytestdata",
"copytestdata": "find tests/output/* -type d -exec cp -R {} bin/tests/output/ \\;",
"test": "npm run cov && npm run covreport",
