Merge pull request ethereum#1572 from hwwhww/hotfix_pyecc

Hotfix: py_ecc==1.4.3

Author: hwwhww

setup.py

@@ -13,7 +13,7 @@
         "eth-utils>=1.3.0b0,<2.0.0",
         "lru-dict>=1.1.6",
         "mypy_extensions>=0.4.1,<1.0.0",
-        "py-ecc>=1.4.2,<2.0.0",
+        "py-ecc==1.4.3",
         "pyethash>=0.1.27,<1.0.0",
         "rlp>=1.0.3,<2.0.0",
         "trie>=1.3.5,<2.0.0",