Update roster spec expectations
Update roster spec expectations

+ Now cells with no data get rendered blank, we add an em dash on the client side

studentinsights/studentinsights,codeforamerica/somerville-teacher-tool,jhilde/studentinsights,studentinsights/studentinsights,jhilde/studentinsights,studentinsights/studentinsights,studentinsights/studentinsights,erose/studentinsights,codeforamerica/somerville-teacher-tool,erose/studentinsights,erose/studentinsights,jhilde/studentinsights,jhilde/studentinsights,codeforamerica/somerville-teacher-tool,codeforamerica/somerville-teacher-tool,erose/studentinsights