extra/runner summary report: Cleanup: Use "plot" for div ID, not "plotdiv"
extra/runner summary report: Cleanup: Use "plot" for div ID, not "plotdiv"

This is for consistency with other IDs like "totals" and "details".

LewisHaley/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester