Specify file encoding for consistency (#35)

Opens for reading already had an `encoding` argument, also added where
opening for writing.

Author: intgr

tests/test_cmd.py

@@ -14,7 +14,7 @@
 
 
 def writefile(path, content):
-    with open(path, 'w') as f:
+    with open(path, 'w', encoding='utf-8') as f:
         f.write(content)
 
 

topy/topy.py

@@ -171,7 +171,7 @@ def handle_file(regs, filename):
     if replaced > 0:
         if opts.apply:
             log.info("Writing %s", safe_name)
-            with open(filename, 'w') as f:
+            with open(filename, 'w', encoding='utf-8') as f:
                 f.write(text)
         else:
             print_diff(safe_name, oldtext, text)