Upgrade to Bootstrap 4

package.json

@@ -25,6 +25,7 @@
     "babel-preset-latest": "^6.24.1",
     "babel-preset-stage-2": "^6.24.1",
     "blackst0ne-mermaid": "^7.1.0-fixed",
+    "bootstrap": "^4.0.0",
     "bootstrap-sass": "^3.3.6",
     "brace-expansion": "^1.1.8",
     "chart.js": "1.0.2",

yarn.lock

@@ -1256,6 +1256,10 @@ bootstrap-sass@^3.3.6:
   version "3.3.6"
   resolved "https://registry.yarnpkg.com/bootstrap-sass/-/bootstrap-sass-3.3.6.tgz#363b0d300e868d3e70134c1a742bb17288444fd1"
 
+bootstrap@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/bootstrap/-/bootstrap-4.0.0.tgz#ceb03842c145fcc1b9b4e15da2a05656ba68469a"
+
 boxen@^1.2.1:
   version "1.3.0"
   resolved "https://registry.yarnpkg.com/boxen/-/boxen-1.3.0.tgz#55c6c39a8ba58d9c61ad22cd877532deb665a20b"