Change minimum treshold and tests for % explained
Fix formatting to use two decimal places

Changing the minimum threshold for an axis to be considered, required us
to change the formatting of the string to have two decimal places,
otherwise it would show 0 for values < to 1.

Fixes #226
Fix error as pointed out by @antgonza
Merge pull request #240 from ElDeveloper/issue-226

Fixes issue 226 - minimum percent explained