Use incremental building when running the local server (#84)

Shaves rebuild time by 4-5x.

Author: JoelMarcey

.gitignore

@@ -6,4 +6,6 @@ vendor
 .sass_cache
 _site
 
-.idea/
+.idea/
+
+.jekyll-metadata

Makefile

@@ -37,7 +37,7 @@ build: install include-yarn-deps
 	$(JEKYLL) build --config _config.yml
 
 serve: install include-yarn-deps
-	JEKYLL_ENV=development $(JEKYLL) serve --config _config.yml
+	JEKYLL_ENV=development $(JEKYLL) serve --incremental --config _config.yml
 
 build_deploy: include-yarn-deps
 	JEKYLL_ENV=production $(JEKYLL) build