add required versions of requirements

requirements.txt

@@ -1,3 +1,4 @@
+configparser>=3.5.0
 coverage
 eth_abi>=1.0.0
 eth-account>=0.1.0a2
@@ -10,6 +11,7 @@ eth-tester>=0.1.0b21
 eth-utils>=1.0.1
 jinja2
 mock
+persistent>=4.2.0
 plyvel
 py-flags
 py-solc
@@ -19,5 +21,3 @@ pytest_mock
 requests
 rlp<1.0.0
 z3-solver>=4.5
-configparser
-persistent

setup.py

@@ -323,8 +323,8 @@ setup(
         'rlp<1.0.0',
         'py-flags',
         'mock',
-        'configparser',
+        'configparser>=3.5.0',
-        'persistent'
+        'persistent>=4.2.0'
     ],
 
     tests_require=[