Don't output every hash onto console, its too slow

Mining is about 3 times faster in average on my computer with this patch.

proofofwork.go

@@ -56,7 +56,9 @@ func (pow *ProofOfWork) Run() (int, []byte) {
 		data := pow.prepareData(nonce)
 
 		hash = sha256.Sum256(data)
-		fmt.Printf("\r%x", hash)
+		if math.Remainder(float64(nonce), 100000) == 0 {
+			fmt.Printf("\r%x", hash)
+		}
 		hashInt.SetBytes(hash[:])
 
 		if hashInt.Cmp(pow.target) == -1 {