build: bump minimum version requirement of gnutls to 3.3.6

This releases offers the gnutls_certificate_set_x509_trust_dir() API we use in
ecore_con. This gnutls version was release in July 2014 which gave it enough
time to be picked up by distributions.

Thanks a lot to llelectronics for reporting and tracking down the problem.

ref T5437
@fix

configure.ac

@@ -388,7 +388,7 @@ AM_CONDITIONAL([EFL_ENABLE_TESTS], [test "${want_tests}" = "yes"])
 # check for crypto/tls library to use
 case "$build_crypto" in
    gnutls)
-      EFL_DEPEND_PKG([crypto], [GNUTLS], [gnutls >= 2.12.16])
+      EFL_DEPEND_PKG([crypto], [GNUTLS], [gnutls >= 3.3.6])
 
       AM_PATH_LIBGCRYPT([], [:],
          [AC_MSG_ERROR([libgcrypt required but not found])])