Use xclip instead of xsel for yanking in copy mode

Sometimes when yanking large blocks of text from a pane larger than its
size in copy mode did not work. Switch to using `xclip` from `xsel` to
see if this works better.

.conduit.yaml

@@ -2,7 +2,7 @@
 - location: ~/.config/tmux
 - apt:
     - tmux
-    - xsel
+    - xclip
     - urlview
 - brew:
     - tmux

tmux.conf

@@ -84,8 +84,8 @@ bind -T copy-mode-vi v send-keys -X begin-selection
 if -b '[ "`uname`" = "Darwin" ]' \
   'bind -T copy-mode-vi y send-keys -X copy-pipe-and-cancel \
     "reattach-to-user-namespace pbcopy"' \
-  'bind -T copy-mode-vi y send-keys -X copy-pipe-and-cancel \
-    "xsel -i -p && xsel -o -p | xsel -i -b"'
+  'bind -T copy-mode-vi y send -X copy-pipe-and-cancel \
+    "xclip -i -sel p -f | xclip -i -sel c"'
 
 # Left status style
 setw -g status-left " #{session_name}"