ci(circle): switch to Julia v0.6.4

The v0.5.2, although it is the version the current Lint.jl is designed 
for, is unable to contact GitHub to download the package. Switch to 
v0.6.4 in order to be able to install the package.

Author: Arcanemagus

.circleci/config.yml

@@ -12,7 +12,7 @@ defaults: &defaults
         name: Install Julia v0.5.2
         command: |
           curl -o julia.tar.gz --location --silent --show-error \
-            https://julialang-s3.julialang.org/bin/linux/x64/0.5/julia-0.5.2-linux-x86_64.tar.gz && \
+            https://julialang-s3.julialang.org/bin/linux/x64/0.6/julia-0.6.4-linux-x86_64.tar.gz && \
           mkdir julia && \
           tar --extract --gzip --strip 1 --directory=julia --file=julia.tar.gz && \
           echo 'export PATH="/home/atom/julia/bin:$PATH"' >> $BASH_ENV