Updates README.md to reflect new lost-column output

* removes the sourcemap (shouldn’t have been there)
* moves the float above the margin

bumbs version to 6.7.1

Merge pull request peterramsing#243 from peterramsing/6.7.0

Releases 6.7.0

🚢 6.6.2

🚢 6.6.1

🚢 6.6.0

Merge pull request peterramsing#148 from iest/master

Make play nice with later postcss plugins

🚢 6.3.0

6.2.0 🚢