fix fish errors

fish/.config/fish/conf.d/fnm.fish

@@ -1,4 +1,4 @@
-if test -n (command -v fnm)
+if test (command -v fnm)
     set PATH /home/nikos/.fnm $PATH
     fnm env | source
 end

fish/.config/fish/conf.d/starship.fish

@@ -1,3 +1,3 @@
-if test -n (command -v starship)
+if test (command -v starship)
     starship init fish | source
 end

fish/.config/fish/conf.d/zoxide.fish

@@ -1,3 +1,3 @@
-if test -n (command -v zoxide)
+if test (command -v zoxide)
     zoxide init fish | source
 end