Fix bug so that the segment separator of left middle has the right color

In short: the current background color was the unfiltered color and is
used to print the next segment separator. If the user set a color like
"purple3" that would result in a white segment separator as Terminal
Emulators do not understand the color "purple3".

powerlevel9k.zsh-theme

@@ -173,7 +173,7 @@ left_prompt_segment() {
   [[ -n "$5" ]] && echo -n "${fg}${5}"
   echo -n "${POWERLEVEL9K_WHITESPACE_BETWEEN_LEFT_SEGMENTS}"
 
-  CURRENT_BG=$3
+  CURRENT_BG="$(getColorCode ${3})"
   last_left_element_index=$current_index
 }