fix: lowercase eth addresses

Ethereum addresses should be all lowercase.  Uppercase chars in ethereum addresses are a sort of optional checksum.  If a program is validating ethereum addresses, random capital letters in the hex string will cause the checksum to fail.

lib/finance.js

@@ -223,7 +223,7 @@ var Finance = function (faker) {
    * @method  faker.finance.ethereumAddress
    */
   self.ethereumAddress = function () {
-    var address = faker.random.hexaDecimal(40);
+    var address = faker.random.hexaDecimal(40).toLowerCase();
 
     return address;
   };