Update ruby

Makefile

@@ -6,11 +6,11 @@ img: assets/img/raw/*
 
 build: img
 	rm -rf _site; exit 0
-	~/.gem/ruby/2.6.0/bin/jekyll build
+	~/.gem/ruby/2.7.0/bin/jekyll build
 	tar -czf blog.tar.gz _site
 
 serve: img
-	~/.gem/ruby/2.6.0/bin/jekyll serve \
+	~/.gem/ruby/2.7.0/bin/jekyll serve \
 		--drafts \
 		--unpublished \
 		--future