allow to use single-character private key, test added

lib/privatekey.js

@@ -103,7 +103,7 @@ PrivateKey.prototype._classifyArguments = function(data, network) {
     info.network = Networks.get(data);
   } else if (typeof(data) === 'string'){
     if (JSUtil.isHexa(data)) {
-      info.bn = new BN(new Buffer(data, 'hex'));
+      info.bn = new BN(data, 'hex');
     } else {
       info = PrivateKey._transformWIF(data, network);
     }

test/privatekey.js

@@ -153,6 +153,13 @@ describe('PrivateKey', function() {
       privkey.publicKey.toString().should.equal(pubhex);
     });
 
+    it('can be instantiated from a single-character hex string', function() {
+      var privhex = '1';
+      var pubhex = '0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798';
+      var privkey = new PrivateKey(privhex);
+      privkey.publicKey.toString().should.equal(pubhex);
+    });
+
     it('should not be able to instantiate because of unrecognized data', function() {
       expect(function() {
         return new PrivateKey(new Error());