Collect more keywords by default

[GunshipPenguin]

We're currently collecting 40 keywords by default, This seems to be a bit low for certain very popular trends as the bottom ranked keywords still have several hundred occurrences, and we could collect more. As an example, here's the keywords array for a trend relating to elections in the UK.

[
        {
            "occurences": 2131,
            "word": "deal"
        },
        {
            "occurences": 2018,
            "word": "#battlefornumber10"
        },
        {
            "occurences": 1494,
            "word": "debate"
        },
        {
            "occurences": 1467,
            "word": "jeremy"
        },
        {
            "occurences": 1396,
            "word": "theresa"
        },
        {
            "occurences": 1193,
            "word": "bollocks"
        },
        {
            "occurences": 1156,
            "word": "scared"
        },
        {
            "occurences": 1083,
            "word": "nhs"
        },
        {
            "occurences": 915,
            "word": "corbyn"
        },
        {
            "occurences": 805,
            "word": "bad"
        },
        {
            "occurences": 698,
            "word": "audience"
        },
        {
            "occurences": 654,
            "word": "question"
        },
        {
            "occurences": 511,
            "word": "funding"
        },
        {
            "occurences": 511,
            "word": "answer"
        },
        {
            "occurences": 508,
            "word": "mouthing"
        },
        {
            "occurences": 485,
            "word": "interview"
        },
        {
            "occurences": 469,
            "word": "police"
        },
        {
            "occurences": 463,
            "word": "won"
        },
        {
            "occurences": 461,
            "word": "member"
        },
        {
            "occurences": 458,
            "word": "manifesto"
        },
        {
            "occurences": 455,
            "word": "brexit"
        },
        {
            "occurences": 452,
            "word": "prime"
        },
        {
            "occurences": 446,
            "word": "makes"
        },
        {
            "occurences": 444,
            "word": "minister"
        },
        {
            "occurences": 439,
            "word": "schools"
        },
        {
            "occurences": 433,
            "word": "collapses"
        },
        {
            "occurences": 433,
            "word": "laugh"
        },
        {
            "occurences": 431,
            "word": "tax"
        },
        {
            "occurences": 421,
            "word": "standing"
        },
        {
            "occurences": 419,
            "word": "guy"
        },
        {
            "occurences": 413,
            "word": "blowhard"
        },
        {
            "occurences": 408,
            "word": "immigration"
        },
        {
            "occurences": 396,
            "word": "sample"
        },
        {
            "occurences": 394,
            "word": "strong"
        },
        {
            "occurences": 390,
            "word": "watching"
        },
        {
            "occurences": 384,
            "word": "paxman"
        },
        {
            "occurences": 378,
            "word": "sign"
        },
        {
            "occurences": 378,
            "word": "summed"
        },
        {
            "occurences": 376,
            "word": "care"
        },
        {
            "occurences": 375,
            "word": "#mayvcorbyn"
        }
]