minor details revised in a gsub

Regexps have a construct to express alternation of characters, which
is character classes. In addition to being the most specific idiom to
write this pattern, it reads better without the backslashes. Also, it
is better not to use a capture if none is needed. As a side-effect of
these changes, the gsub is marginally faster, but speed is not the
point of this commit.

actionpack/lib/action_view/template/resolver.rb

@@ -164,7 +164,7 @@ def build_query(path, details)
     end
 
     def escape_entry(entry)
-      entry.gsub(/(\*|\[|\]|\{|\}|\?)/, "\\\\\\1")
+      entry.gsub(/[*?{}\[\]]/, '\\\\\\&')
     end
 
     # Returns the file mtime from the filesystem.