Broken image and title consistency

[EmmaJP]

Hopefully a quick one to fix...

https://bbc.github.io/gel/foundations/iconography/ appears to have a broken image within the "Colour independence" part, at the start of the last paragraph "Movement on...".

Also, the page is headed "Iconography". This is reflected in the URL, but not the link to the page on the site homepage that uses "Icons".