Upgrade bootstrap to 4.3.1 (#29)

package.json

@@ -11,7 +11,7 @@
     "babel-loader": "7.1.2",
     "babel-preset-react-app": "^3.1.2",
     "babel-runtime": "6.26.0",
-    "bootstrap": "4.2.1",
+    "bootstrap": ">=4.3.1",
     "case-sensitive-paths-webpack-plugin": "2.1.1",
     "chalk": "1.1.3",
     "chroma-js": "^1.4.0",

yarn.lock

@@ -1243,10 +1243,10 @@ boolbase@~1.0.0:
   resolved "https://registry.yarnpkg.com/boolbase/-/boolbase-1.0.0.tgz#68dff5fbe60c51eb37725ea9e3ed310dcc1e776e"
   integrity sha1-aN/1++YMUes3cl6p4+0xDcwed24=
 
-bootstrap@4.2.1:
-  version "4.2.1"
-  resolved "https://registry.yarnpkg.com/bootstrap/-/bootstrap-4.2.1.tgz#8f8bdca024dbf0e8644da32e918c8a03a90a5757"
-  integrity sha512-tt/7vIv3Gm2mnd/WeDx36nfGGHleil0Wg8IeB7eMrVkY0fZ5iTaBisSh8oNANc2IBsCc6vCgCNTIM/IEN0+50Q==
+bootstrap@>=4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/bootstrap/-/bootstrap-4.3.1.tgz#280ca8f610504d99d7b6b4bfc4b68cec601704ac"
+  integrity sha512-rXqOmH1VilAt2DyPzluTi2blhk17bO7ef+zLLPlWvG494pDxcM234pJ8wTc/6R40UWizAIIMgxjvxZg5kmsbag==
 
 boxen@^1.2.1:
   version "1.3.0"