Fix multiline case statement

Oozie users usually write case statement as follows:

~~~xml
<switch>
            <case to="foo">
              	${wf:actionData('bar')['baz'] == 1} 
            </case>             
            <default to="join"/>
        </switch>
~~~

A such entry lead vizoozie to generate an invalid DOT file. This pull request fix this issue. I decided to join all the lines  since I never saw a huge EL expression in a case statement.