Update android.py, changed encode --> decode

In recreate the project.properties section, changed:
line.encode('utf-8') --> line.decode('utf-8') 
so that "android_old" option can work, otherwise it exits with an exception after creating an empty "project.properties" file

buildozer/targets/android.py

@@ -851,7 +851,7 @@ class TargetAndroid(Target):
         # recreate the project.properties
         with io.open(project_fn, 'w', encoding='utf-8') as fd:
             try:
-                fd.writelines((line.encode('utf-8') for line in content))
+                fd.writelines((line.decode('utf-8') for line in content))
             except:
                 fd.writelines(content)
             if not content[-1].endswith(u'\n'):