Pkg.build fails on 0.5.2 (linux)

[lobingera]

               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.2 (2017-05-06 16:34 UTC)
 _/ |\__'_|_|_|\__'_|  |  
|__/                   |  x86_64-linux-gnu

julia> Pkg.add("WinRPM")
INFO: Nothing to be done

julia> Pkg.build("WinRPM")
INFO: Building LibCURL
INFO: Building WinRPM
WARNING: Method definition get(AbstractString) in module HTTPC at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:379 overwritten at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:534.
WARNING: Method definition head(AbstractString) in module HTTPC at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:511 overwritten at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:534.
WARNING: Method definition delete(AbstractString) in module HTTPC at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:528 overwritten at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:534.
WARNING: Method definition trace(AbstractString) in module HTTPC at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:529 overwritten at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:534.
WARNING: Method definition options(AbstractString) in module HTTPC at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:530 overwritten at /home/lobi/.julia/v0.5/HTTPClient/src/HTTPC.jl:534.
WARNING: skipping repodata/repomd.xml, not in cache -- call WinRPM.update() to download
WARNING: skipping repodata/repomd.xml, not in cache -- call WinRPM.update() to download
INFO: Downloading https://cache.julialang.org/http://download.opensuse.org/repositories/windows:/mingw:/win32/openSUSE_Leap_42.2/repodata/repomd.xml
===============================[ ERROR: WinRPM ]================================

LoadError: MethodError: no method matching unsafe_string(::Base.AbstractIOBuffer{Array{UInt8,1}})
Closest candidates are:
  unsafe_string(::Cstring) at c.jl:187
  unsafe_string(::Union{Ptr{Int8},Ptr{UInt8}}) at strings/basic.jl:56
  unsafe_string(::Union{Ptr{Int8},Ptr{UInt8}}, ::Integer) at strings/basic.jl:52
while loading /home/lobi/.julia/v0.5/WinRPM/deps/build.jl, in expression starting on line 2

================================================================================

================================[ BUILD ERRORS ]================================

WARNING: WinRPM had build errors.

 - packages with build errors remain installed in /home/lobi/.julia/v0.5
 - build the package(s) and all dependencies with `Pkg.build("WinRPM")`
 - build a single package by running its `deps/build.jl` script

================================================================================

i'm trying to debug a win32 installation issue on an appveyor test and will use WinRPM locally (on a linux box) to download and extract.