audit: only look for empty checksums once

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/audit.rb

@@ -75,18 +75,10 @@ def audit_formula_text name, text
   end
 
   # Empty checksums
-  if text =~ /md5\s+(''|"")/
+  if text =~ /(md5|sha1|sha256)\s+(''|"")/
     problems << " * md5 is empty"
   end
 
-  if text =~ /sha1\s+(''|"")/
-    problems << " * sha1 is empty"
-  end
-
-  if text =~ /sha256\s+(''|"")/
-    problems << " * sha256 is empty"
-  end
-
   # Checksum sanity check
   if text =~ /md5\s+['"](.+)['"]/ and $1 != '#{md5}' and $1 !~ /[a-f0-9]{32}/
     problems << " * md5 contains invalid or incorrect number of characters"