Handle nils in words lists better

[marshall-prosperworks]

Our automated tests use RandomWord to generate test data, but there is a nil in the adjectives list. This causes some small proportion of our tests to fail when exclude? hits the sub-expression word.length on line 61.

[coveralls]

Coverage remained the same at 100.0% when pulling 581affb on marshall-prosperworks:remove-null-from-adjectives-list into c6852fe on openlogic:master.

[kinduff]

Thanks for this!

[d00rsfan]

Owner should add to documentation that gem produce a lot of
random_word.rb:61:in excluded?': undefined method length' for nil:NilClass (NoMethodError)
So community will not be waste time with it and move forward.