Update Solution argument names to match prompt

[pyamin1878]

Here is the function signature of the prompt:

def multi_word_search(doc_list, keywords):

Here is the function when you print out the solution:

def multi_word_search(documents, keywords):
    keyword_to_indices = {}
    for keyword in keywords:
        keyword_to_indices[keyword] = word_search(documents, keyword)
    return keyword_to_indices

This pr will make the function consistent with the provided exercise.

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