Update agnoster to use new powerline codepoints

See https://github.com/Lokaltog/powerlin://github.com/Lokaltog/powerline
and http://lokaltog.github.com/powerline/fontpatching.html

themes/agnoster.zsh-theme

@@ -26,7 +26,7 @@
 # A few utility functions to make it easy and re-usable to draw segmented prompts
 
 CURRENT_BG='NONE'
-SEGMENT_SEPARATOR='⮀'
+SEGMENT_SEPARATOR=''
 
 # Begin a segment
 # Takes two arguments, background and foreground. Both can be omitted,
@@ -79,7 +79,7 @@ prompt_git() {
     else
       prompt_segment green black
     fi
-    echo -n "${ref/refs\/heads\//⭠ }$dirty"
+    echo -n "${ref/refs\/heads\// }$dirty"
   fi
 }