update version to 0.1.8

Changes since version 0.1.7
* Refactor browser building
* Examples of signing transactions
* Key interface is now bitcore.Key, not bitcore.KeyModule.Key
** bitcore.KeyModule is deprecated
* Bug fixes

package.json

@@ -1,7 +1,7 @@
 {
   "name": "bitcore",
   "description": "Bitcoin Library",
-  "version": "0.1.7",
+  "version": "0.1.8",
   "author": {
     "name": "Stephen Pair",
     "email": "stephen@bitpay.com"