Upgrade eth-tester

Author: kclowes

setup.py

@@ -7,7 +7,7 @@
 
 extras_require = {
     'tester': [
-        "eth-tester[py-evm]==0.1.0-beta.37",
+        "eth-tester[py-evm]==0.1.0-beta.39",
         "py-geth>=2.0.1,<3.0.0",
         "pytest-ethereum>=0.1.3a6,<1.0.0",
     ],