Fix ambiguity warning on master

Caused by https://github.com/JuliaLang/julia/issues/14935

Cc: @vtjnash

Noted here:

julia> Pkg.test("GZip")
INFO: Testing GZip
WARNING: New definition
    write(GZip.GZipStream, Array{#T<:Any, N<:Any}) at /Users/kmsquire/.julia/v0.5/GZip/src/GZip.jl:456
is ambiguous with:
    write(Base.IO, Array{UInt8, N<:Any}) at io.jl:154.
To fix, define
    write(GZip.GZipStream, Array{UInt8, N<:Any})
before the new definition.

Version info:

julia> versioninfo()
Julia Version 0.5.0-dev+2440
Commit 2bb94d6 (2016-02-01 02:22 UTC)
Platform Info:
  System: Darwin (x86_64-apple-darwin13.4.0)
  CPU: Intel(R) Core(TM)2 Extreme CPU X7900  @ 2.80GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Core2)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.7.1

JuliaIO / GZip.jl

Fix ambiguity warning on master #47