Fixes for jekyll 4.0.0.

.gitignore

@@ -1,5 +1,6 @@
 _site/
 .sass-cache/
+.jekyll-cache/
 
 # Windows image file caches
 Thumbs.db

.gitlab-ci.yml

@@ -1,6 +1,6 @@
 # This file is a template, and might need editing before it works on your project.
 # Full project: https://gitlab.com/pages/jekyll
-image: ruby:2.4
+image: ruby:2.6
 
 test:
   stage: test
@@ -16,7 +16,7 @@ test:
 pages:
   stage: deploy
   script:
-  - gem install jekyll jekyll-sitemap
+  - gem install jekyll jekyll-sitemap forwardable --version 1.2.0
   - jekyll build -d public --future
   artifacts:
     paths:

_assets/core.scss

@@ -12,5 +12,3 @@
 
 @import 'main';
 @import 'syntax';
-
-

_sass/main.css

@@ -1 +0,0 @@
-main.scss