Fixing PATH when using brew plugin

plugins/brew/brew.load.fish

+function _path_index
+  if test $PATH[$argv[1]] = $argv[2]
+    echo 'Path index correct'
+  end
+end
+
+# Set /usr/local/bin before /usr/bin if defined on $PATH
+if contains /usr/local/bin $PATH
+  if contains /usr/bin $PATH
+    for i in (seq (count $PATH))
+      if test (_path_index $i '/usr/bin')
+        set -g bin_index $i
+      else
+        if test (_path_index $i '/usr/local/bin')
+          set -g local_bin_index $i
+        end
+      end
+    end
+
+    if test $bin_index -lt $local_bin_index
+      set PATH[$bin_index] /usr/local/bin
+      set PATH[$local_bin_index] /usr/bin
+    end
+  end
+end
+
+set -e bin_index
+set -e local_bin_index