remove redundant pytest requirement and sort requirements file

requirements.txt

@@ -1,24 +1,23 @@
-rlp<1.0.0
-ethereum>=2.3.0
-ZODB>=5.3.0
-z3-solver>=4.5
-requests
 BTrees
-plyvel
-py-solc
-pytest>=3.6.0
+coverage
 eth_abi>=1.0.0
-eth-utils>=1.0.1
 eth-account>=0.1.0a2
+ethereum>=2.3.0
 eth-hash>=0.1.0
 eth-keyfile>=0.5.1
 eth-keys>=0.2.0b3
 eth-rlp>=0.1.0
 eth-tester>=0.1.0b21
-coverage
+eth-utils>=1.0.1
 jinja2
-pytest
-py-flags
 mock
-pytest_mock
+plyvel
+py-flags
+py-solc
+pytest>=3.6.0
 pytest-cov
+pytest_mock
+requests
+rlp<1.0.0
+z3-solver>=4.5
+ZODB>=5.3.0