Use colon in "%YAML:1.0" directive when persisting to YAML-files

In YAML 1.0 the colon is mandatory. See http://yaml.org/spec/1.0/#id2558635.

This also allows prior releases to read YAML files created with the current version.

modules/core/src/persistence.cpp

@@ -4332,7 +4332,7 @@ cvOpenFileStorage( const char* query, CvMemStorage* dststorage, int flags, const
         else if( fs->fmt == CV_STORAGE_FORMAT_YAML )
         {
             if( !append )
-                icvPuts( fs, "%YAML 1.0\n---\n" );
+                icvPuts( fs, "%YAML:1.0\n---\n" );
             else
                 icvPuts( fs, "...\n---\n" );
             fs->start_write_struct = icvYMLStartWriteStruct;