Update gr.jl in v0.6 so inline plots work

I wanted to switch from using GR directly to using Plots, but the inline plots were not working for me. The following change is sufficient to generate inline plots in iterm for me.

See the method in GR.jl:
https://github.com/jheinen/GR.jl/blob/0f167b2be921a0014c405f760a1e1bc22b222751/src/GR.jl#L3014

julia> versioninfo()
Julia Version 0.6.0-pre.beta.187
Commit 55c97fb* (2017-04-17 23:06 UTC)
Platform Info:
OS: Linux (x86_64-redhat-linux)
CPU: Intel(R) Xeon(R) CPU E5-2670 v3 @ 2.30GHz
WORD_SIZE: 64
BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
LAPACK: libopenblas64_
LIBM: libopenlibm
LLVM: libLLVM-3.9.1 (ORCJIT, haswell)


julia> using TerminalExtensions
julia> using Plots
julia> gr(display_type=:inline);
julia> z=[sin(sqrt(x^2+y^2)) for x in linspace(-2π,2π,50), y in linspace(-2π,2π,50)];
julia> contour(z)

src/backends/gr.jl

@@ -1101,7 +1101,7 @@ function _display(plt::Plot{GRBackend})
         ENV["GKS_FILEPATH"] = filepath
         gr_display(plt)
         GR.emergencyclosegks()
-        content = string("\033]1337;File=inline=1;preserveAspectRatio=0:", base64encode(open(readbytes, filepath)), "\a")
+        content = string("\033]1337;File=inline=1;preserveAspectRatio=0:", base64encode(open(read, filepath)), "\a")
         println(content)
         rm(filepath)
     else