FIX: Restricts `eth-account` package version to be <=0.3.0

Because `eth-account@0.4.0` depends on `eth_abi>=2.0.0b7`, which
conflicts with `eth_abi==1.3.0` required by `mythril-classic`. As I am
looking for a rapid fix, I am restricting `eth-account<=0.3.0` rather
than trying to allow higher versions of `eth_abi`. Thus, leaving to
`mythril-classic` team to inverstigate possibility of update to latest
`eth-account` and `eth_abi`, and fix any related issues.

requirements.txt

@@ -3,7 +3,7 @@ configparser>=3.5.0
 coverage
 py_ecc==1.4.2
 eth_abi==1.3.0
-eth-account>=0.1.0a2
+eth-account>=0.1.0a2,<=0.3.0
 ethereum>=2.3.2
 ethereum-input-decoder>=0.2.2
 eth-hash>=0.1.0

setup.py

@@ -81,7 +81,7 @@ setup(
         "plyvel",
         "eth_abi==1.3.0",
         "eth-utils>=1.0.1",
-        "eth-account>=0.1.0a2",
+        "eth-account>=0.1.0a2,<=0.3.0",
         "eth-hash>=0.1.0",
         "eth-keyfile>=0.5.1",
         "eth-keys>=0.2.0b3",