Update API.md

Minor typo fix
Merge pull request #676 from jeteon/patch-1

Update API.md
Remove explicit use of ./node_modules/.bin

npm's "scripts" functionality automatically adds executables from required libraries to the path when invoked.

Hence, there is no need to use the explicit "./node_modules/.bin/mocha" as just "mocha" will do.
Merge pull request #677 from bruce-one/patch-1

Remove explicit use of ./node_modules/.bin