nixos/shells: fix indent everywhere

to comply with `doc/coding-conventions.xml`

nixos/modules/programs/zsh/zsh.nix

@@ -70,7 +70,7 @@ in
       promptInit = mkOption {
         default = ''
           if [ "$TERM" != dumb ]; then
-            autoload -U promptinit && promptinit && prompt walters
+              autoload -U promptinit && promptinit && prompt walters
           fi
         '';
         description = ''
@@ -113,7 +113,7 @@ in
 
         # Read system-wide modifications.
         if test -f /etc/zshenv.local; then
-          . /etc/zshenv.local
+            . /etc/zshenv.local
         fi
       '';
 
@@ -132,7 +132,7 @@ in
 
         # Read system-wide modifications.
         if test -f /etc/zprofile.local; then
-          . /etc/zprofile.local
+            . /etc/zprofile.local
         fi
       '';
 
@@ -158,7 +158,7 @@ in
 
         # Tell zsh how to find installed completions
         for p in ''${(z)NIX_PROFILES}; do
-          fpath+=($p/share/zsh/site-functions $p/share/zsh/$ZSH_VERSION/functions $p/share/zsh/vendor-completions)
+            fpath+=($p/share/zsh/site-functions $p/share/zsh/$ZSH_VERSION/functions $p/share/zsh/vendor-completions)
         done
 
         ${optionalString cfg.enableCompletion "autoload -U compinit && compinit"}
@@ -173,7 +173,7 @@ in
 
         # Read system-wide modifications.
         if test -f /etc/zshrc.local; then
-          . /etc/zshrc.local
+            . /etc/zshrc.local
         fi
       '';