correct Documenter version

Author: abhinavmehndiratta

.travis.yml

@@ -8,5 +8,5 @@ julia:
   - 1.0
 
 after_success:
-    - julia -e 'using Pkg; ps=Pkg.PackageSpec(name="Documenter", version="0.19"); Pkg.add(ps); Pkg.pin(ps)'
+    - julia -e 'using Pkg; ps=Pkg.PackageSpec(name="Documenter", version="0.22"); Pkg.add(ps); Pkg.pin(ps)'
     - julia -e 'using Pkg; cd(Pkg.dir("SuiteSparseGraphBLAS")); include(joinpath("docs", "make.jl"))'