Update travis configuration and some error message

.travis.yml

@@ -10,7 +10,7 @@ php:
 
 env:
   global:
-    - ARMA_VERSION="9.600.5"
+    - ARMA_VERSION="9.600.6"
     - ARMA_SRC="http://sourceforge.net/projects/arma/files/armadillo-${ARMA_VERSION}.tar.xz"
 
 before_install:

src/stream_utils.hh

@@ -56,7 +56,7 @@ namespace php_arma
     void zval_to_iostream_unsupported()
     {
         throw_exception_ex(zend_ce_type_error, "resource is not yet supported, use file name instead, "
-            "or re-compile php-armadillo with a compiler supporting GNU extensions");
+            "or re-compile php-armadillo and link with libstdc++ instead of other STL implmentations.");
     }
 
     constexpr auto zval_to_iostream_supported = false;