Bump minimum supported Zsh to v4.3.11

zsh-syntax-highlighting requires this version.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>

README.md

@@ -9,7 +9,7 @@ Installation
 ------------
 
 Prezto will work with any recent release of Zsh, but the minimum recommended
-version is 4.3.11.
+version is 4.3.17.
 
   1. Launch Zsh:
 

init.zsh

@@ -10,7 +10,7 @@
 #
 
 # Check for the minimum supported version.
-min_zsh_version='4.3.11'
+min_zsh_version='4.3.17'
 if ! autoload -Uz is-at-least || ! is-at-least "$min_zsh_version"; then
   print "prezto: old shell detected, minimum required: $min_zsh_version" >&2
   return 1