[inference] poor Promise.race inference

[Andarist]

https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoAxnAdgZwC5gAmApjAIYCeYAvGABQC2OANGAG5kwCUNAfGFmJIACgCc4DAJY5idUcRxwYbYnzABvVGDAy8AFUkNicAK546dHtX7zFy2R26smXVAF9XGbPjAAHAII0RKSUdACMAAwRrABEZDgxrpi4BL4AQkEk5BThUax4oibEnmIS0sQAdKJk6LIA2gGs6QC6XBV4ABbEWHSOan0A1OycrqVSMlU19Y1+-q3tXT191sMwYEOOXEA

In contrast to TypeScript

http://www.typescriptlang.org/play/#src=const%20delay%20%3D%20%3CT%3E(ms%3A%20number%2C%20val%3A%20T)%3A%20Promise%3CT%3E%20%3D%3E%20new%20Promise(resolve%20%3D%3E%20%7B%0D%0A%20%20setTimeout(()%20%3D%3E%20resolve(val)%2C%20ms)%0D%0A%7D)%0D%0A%0D%0Aconst%20pA%20%3D%20delay(100%2C%20%22as%22)%0D%0Aconst%20pB%20%3D%20delay(100%2C%20true)%0D%0A%0D%0APromise.race(%5BpA%2C%20pB%5D).then(val%20%3D%3E%20val%20%2B%20val)%0D%0APromise.race(%5BpA%2C%20pA%5D).then(val%20%3D%3E%20val%20%2B%20val)%0D%0A

[Andarist]

The issue can be mitigated by adding a generic to the function (like this), but imho it should be possible to infer this without it.