Update filter construction to make it greedy. For example, if we are
    in the path:
    
            trunk/Identity/Themes/Motifs/TreeFlower/4/Distro/5/Anaconda/
            |-- 01-welcome.png
            |-- 02-donate.png
            |-- 03-yum.png
            |-- 04-repos.png
            |-- 05-centosplus.png
            |-- 06-support.png
            |-- 07-docs.png
            |-- 08-wiki.png
            |-- 09-virtualization.png
            |-- anaconda_header.png
            |-- first.png
            `-- splash.png
    
            the following two commands will render the `01-welcome.png'
            file:
    
            centos-art render . --filter='01'
            centos-art render . --filter='01-welcome'
    
            otherwise, it would be required to provide the full filename,
            as we did in the last command (i.e., the first command
            wouldn't match).