needs update for string.data changes

[stevengj]

After JuliaLang/julia#19449, soon to be merged for Julia 0.6, you will no longer be able to access the raw bytes of a string via string.data; instead, do Vector{UInt8}(string). For example, this affects:

https://github.com/nolta/ICU.jl/blob/cbc2d74e020d4f7935498d52bbbffb3a98cce6d0/src/ICU.jl#L166

[stevengj]

Note that in that line you can just pass str, sizeof(str) instead of str.data, sizeof(str.data).