Ensure to run ESLint on automatically ignored dotfiles

The ignore pattern for dotfiles it automatically applied by ESLint to
prevent accidentally lint over paths like ".cache", ".git" or any other
critical paths. Explicitly excluding dotfiles from the ignore pattern
allows to lint these files.

GH-15

.eslintignore

@@ -11,3 +11,7 @@ content/*
 **/node_modules/*
 public/*
 static/*
+!.gatsby
+!.eslintrc.js
+!.huskyrc.js
+!.remarkrc.js