Add `_.nthArg` tests.
Add `_.nthArg` tests.

boneskull/lodash,steelsojka/lodash,Xotic750/lodash,steelsojka/lodash,rlugojr/lodash,Xotic750/lodash,Xotic750/lodash,beaugunderson/lodash,tonyonodi/lodash,beaugunderson/lodash,rlugojr/lodash,boneskull/lodash,msmorgan/lodash,msmorgan/lodash,tonyonodi/lodash