chore(package): update ganache-core to version 2.6.0

Closes #59

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
     "@digix/tempo": "0.2.0",
     "chai": "4.1.2",
     "ethereumjs-wallet": "0.6.2",
-    "ganache-core": "2.5.5",
+    "ganache-core": "2.6.0",
     "mocha": "5.1.1",
     "truffle-contract": "3.0.6",
     "web3": "0.20.7"