environment: Simplify nested conditional block

Avoid unnecessary nesting for conditional block.

modules/environment/init.zsh

@@ -18,12 +18,10 @@ if [[ ${ZSH_VERSION} != 5.1.1 && ${TERM} != "dumb" ]]; then
   if is-at-least 5.2; then
     autoload -Uz bracketed-paste-url-magic
     zle -N bracketed-paste bracketed-paste-url-magic
-  else
+  elif is-at-least 5.1; then
-    if is-at-least 5.1; then
     autoload -Uz bracketed-paste-magic
     zle -N bracketed-paste bracketed-paste-magic
   fi
-  fi
   autoload -Uz url-quote-magic
   zle -N self-insert url-quote-magic
 fi