Merge pull request #132 from JuliaGaussianProcesses/compathelper/new_version/2020-07-01-00-20-09-791-3133309910

CompatHelper: bump compat for "Documenter" to "0.25" for package docs

Author: theogf

docs/Project.toml

@@ -2,4 +2,4 @@
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 
 [compat]
-Documenter = "0.23, 0.24"
+Documenter = "0.23, 0.24, 0.25"