keg_relocate: fix ordering of replacements

Library/Homebrew/keg_relocate.rb

@@ -66,7 +66,14 @@ class Keg
         relocation.old_repository => relocation.new_repository,
       }
 
-      regexp = Regexp.union(replacements.keys)
+      # Order matters here since `HOMEBREW_CELLAR` and `HOMEBREW_REPOSITORY` are
+      # children of `HOMEBREW_PREFIX` by default.
+      regexp = Regexp.union(
+        relocation.old_cellar,
+        relocation.old_repository,
+        relocation.old_prefix
+      )
+
       changed = s.gsub!(regexp, replacements)
 
       next unless changed