bump travis to julia-1.5

Author: denizyuret

.travis.yml

@@ -7,7 +7,7 @@ os:
   - osx
 
 julia:
-  - 1.4
+  - 1.5
   - nightly
 
 notifications:
@@ -16,7 +16,7 @@ notifications:
 jobs:
   include:
       - stage: "Documentation"
-        julia: 1.4
+        julia: 1.5
         os: linux
         script:
           - julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.build("Knet"); Pkg.instantiate()'