Update pipenv-to-pip to read lockfiles properly

Use the appropriate encoding to read a Pipfile.lock so we can
properly load the data.

Closes #678

vendor/pipenv-to-pip

@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 
+import io
 import json
 import sys
 
@@ -7,7 +8,7 @@ import sys
 def main():
     INFILE = sys.argv[1]
 
-    with open(INFILE, 'rb') as f:
+    with io.open(INFILE, 'r', encoding='utf-8') as f:
         lockfile = json.load(f)
 
     packages = []