coerce* in types submodule silenly returns nil if coercion failed

[no1seman]

coerceInt, coerceLong, coerceFloat, coerceBoolean, coerceString - silenly returns nil if coesion failed:

graphql/graphql/types.lua

Line 263 in 58b64a6

if not isInt(value) then return end

graphql/graphql/types.lua

Line 302 in 58b64a6

if not isLong(value) then return end

graphql/graphql/types.lua

Line 346 in 58b64a6

if not isFloat(value) then return end

Seems it wiil better to raise an error if coercion failed (to be discussed)

[no1seman]

Also pay attention to this comment: #55 (comment)