docs/julia/index.md: update link to FactCheck.jl (#497)

https://github.com/JuliaAttic/FactCheck.jl hasn't been updated in years and doesn't work with current Julia versions

Author: jcsahnwaldt

content/languages/julia/index.md

@@ -17,7 +17,7 @@ Beta
 
 ## Test Frameworks
 
-[FactCheck](https://github.com/JuliaArchive/FactCheck.jl)
+[FactCheck](https://github.com/codewars/FactCheck.jl)
 
 ### Minimum Example
 ```julia