I would be fine dropping support for 0.5 altogether but the error seems to be unrelated to the package code:
The error appears to be in cloning the METADATA repo:
$ julia --color=yes -e "VERSION >= v\"0.7.0-DEV.5183\" && using Pkg; Pkg.clone(pwd()); Pkg.build(\"${JL_PKG}\")"
INFO: Initializing package repository /home/travis/.julia/v0.5
INFO: Cloning METADATA from https://github.com/JuliaLang/METADATA.jl
ERROR: GitError(Code:ERROR, Class:Net, SSL error: error:1407742E:SSL routines:SSL23_GET_SERVER_HELLO:tlsv1 alert protocol version)
in macro expansion at ./libgit2/error.jl:99 [inlined]
in clone(::String, ::String, ::Base.LibGit2.CloneOptions) at ./libgit2/repository.jl:191
in #clone#112(::String, ::Bool, ::Ptr{Void}, ::Nullable{Base.LibGit2.AbstractCredentials}, ::Function, ::String, ::String) at ./libgit2/libgit2.jl:327
in (::Base.LibGit2.#kw##clone)(::Array{Any,1}, ::Base.LibGit2.#clone, ::String, ::String) at ./<missing>:0
in (::Base.Pkg.Dir.##4#6{String,String})() at ./pkg/dir.jl:49
in cd(::Base.Pkg.Dir.##4#6{String,String}, ::String) at ./file.jl:59
in init(::String, ::String) at ./pkg/dir.jl:47
in #cd#1(::Array{Any,1}, ::Function, ::Function, ::String, ::Vararg{Any,N}) at ./pkg/dir.jl:28
in clone(::String) at ./pkg/pkg.jl:151
in eval(::Module, ::Any) at ./boot.jl:234
in process_options(::Base.JLOptions) at ./client.jl:242
in _start() at ./client.jl:321
This doesn’t happen in 0.6 and above, and previous builds have succeeded for 0.5. I’ve tried restarting the job several times but the result is always the same. Could this perhaps be some change in METADATA.jl that got backported to 0.6 but not to 0.5?