update mnemonic requirement

requirements.txt

@@ -1,4 +1,4 @@
 ecdsa>=0.9
 protobuf>=2.6.1
-mnemonic>=0.16
+mnemonic>=0.17
 hidapi>=0.7.99

setup.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 from setuptools import setup
 
-install_requires = ['ecdsa>=0.9', 'protobuf>=2.6.1', 'mnemonic>=0.16', 'setuptools>=19.0']
+install_requires = ['ecdsa>=0.9', 'protobuf>=2.6.1', 'mnemonic>=0.17', 'setuptools>=19.0']
 
 import sys
 if '--disable-hidapi' in sys.argv: