cqlsh copy uses wrong variable name for time_format

diff --git a/bin/cqlsh b/bin/cqlsh
index ca45be3..ddf0314 100755
--- a/bin/cqlsh
+++ b/bin/cqlsh
@@ -1816,7 +1816,7 @@ class Shell(cmd.Cmd):
         encoding = opts.pop('encoding', 'utf8')
         nullval = opts.pop('null', '')
         header = bool(opts.pop('header', '').lower() == 'true')
-        timestamp_format = opts.pop('time_format', self.display_timestamp_format)
+        timestamp_format = opts.pop('time_format', self.display_time_format)
         if dialect_options['quotechar'] == dialect_options['escapechar']:
             dialect_options['doublequote'] = True
             del dialect_options['escape char']