Change double quotes to single quotes

Author: prep

examples/balance.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 
 import sys, os 
-sys.path.append(os.path.join(os.path.dirname(__file__), ".."))  
+sys.path.append(os.path.join(os.path.dirname(__file__), '..'))
 
 import messagebird