Fix #55, change to let expr syntax in julia v0.7

[jmert]

This fixes #55 and makes the package tests complete again on julia master.

Also appears to fix #54.

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  | | |_| | | | (_| |  |  Version 0.7.0-DEV.1725 (2017-09-08 14:58 UTC)
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julia> Pkg.test("MacroTools")
INFO: Testing MacroTools
...

WARNING: deprecated syntax "parametric method syntax foo{}(x,; )::Any around /home/justin/.julia/v0.7/MacroTools/src/utils.jl:245".
Use "foo(x,; ) where {}" instead.

WARNING: deprecated syntax "parametric method syntax add{}(a, b = 2; c = 3, d = 4)::Float64 around /home/justin/.julia/v0.7/MacroTools/src/utils.jl:245".
Use "add(a, b = 2; c = 3, d = 4) where {}" instead.

WARNING: deprecated syntax "parametric method syntax fparam{T}(a::T,; )::Any around /home/justin/.julia/v0.7/MacroTools/src/utils.jl:245".
Use "fparam(a::T,; ) where T" instead.

WARNING: deprecated syntax "parametric method syntax ::Orange{}(x,; )::Any around /home/justin/.julia/v0.7/MacroTools/src/utils.jl:245".
Use "false(x,; ) where {}" instead.

WARNING: deprecated syntax "parametric method syntax fwhere{T}(a::T,; )::Any around /home/justin/.julia/v0.7/MacroTools/src/utils.jl:245".
Use "fwhere(a::T,; ) where T" instead.
INFO: MacroTools tests passed

[jmert]

Looks like the tests on master/nightly are now failing due to a macro issue already reported in JuliaLang/julia#23661.

[MikeInnes]

Thanks a lot for the patch. Hope you don't mind me taking #57 just because it's a bit more complete.

[jmert]

Closed/Made obsolete by #57