add missing test to sum of multiples exercise
add missing test to sum of multiples exercise

outkaj/xpython,rootulp/xpython,behrtam/xpython,orozcoadrian/xpython,pheanex/xpython,smalley/python,outkaj/xpython,de2Zotjes/xpython,N-Parsons/exercism-python,de2Zotjes/xpython,jmluy/xpython,orozcoadrian/xpython,rootulp/xpython,oalbe/xpython,exercism/python,pheanex/xpython,oalbe/xpython,exercism/xpython,behrtam/xpython,N-Parsons/exercism-python,jmluy/xpython,exercism/python,smalley/python,mweb/python,exercism/xpython,mweb/python