Merge pull request #18 from walkerflocker/master

fixed type errors

blockchain.py

@@ -90,7 +90,7 @@ class Blockchain:
 
         return False
 
-    def new_block(self, proof, previous_hash):
+    def new_block(self, proof: int, previous_hash: Optional[str]=None) -> Dict[str, Any]:
         """
         Create a new Block in the Blockchain
 
@@ -131,7 +131,7 @@ class Blockchain:
         return self.last_block['index'] + 1
 
     @property
-    def last_block(self):
+    def last_block(self) -> Dict[str, Any]:
         return self.chain[-1]
 
     @staticmethod