removing unused dep

Author: nsjames

package.json

@@ -93,7 +93,6 @@
     "secp256k1": "^3.6.2",
     "semver": "^5.5.1",
     "sha3": "^2.0.2",
-    "shelljs": "^0.7.6",
     "sinon": "^4.0.0",
     "sinon-chai": "^2.8.0",
     "spectron": "^5.0.0",