Fix APK signing on osx.

Author: jvennix-r7

lib/msf/core/payload/dalvik.rb

@@ -60,6 +60,7 @@ def generate_cert
     # with a key whose validity expires before that date.
     # """
     cert.not_after = cert.not_before + 3600*24*365*20 # 20 years
+    cert.sign(key, OpenSSL::Digest::SHA1.new)
     return cert, key
   end
 end