(Reuters) - AbbVie Inc posted quarterly sales above estimates on Friday and raised the lower end of its 2019 profit forecast, helped by strong demand for cancer medicine Imbruvica and a lower-than-expected drop in bestseller Humira's revenue.In June, AbbVie announced a $63 billion (£49 billion) deal for Botox-maker Allergan Plc , in a bid to diversify its drug pipeline amid growing threats to Humira's longevity.The world's top-selling drug, which treats rheumatoid arthritis and psoriasis, has..