Update README version badge to point to releases

[jeroenptrs]

Fixes #61

Problem

See #61

Solution

Renamed tags/tag to releases/release (as per shields.io documentation)

Notes

• [x] Remember to bump the VERSION file using semver 📝
• [x] Make sure the CI tests pass on your branch 👍

[revett]

@jeroenptrs Thought it would be easier for you to bump the version.

[jeroenptrs]

@revett done!