chore: Update bootstrap-sass (jquense#2136)

Update resolves the deprecation warnings coming from the dart-sass compiler

.size-snapshot.json

@@ -1,25 +1,25 @@
 {
   "./dist/react-big-calendar.js": {
-    "bundled": 536878,
-    "minified": 165661,
-    "gzipped": 51020
+    "bundled": 539571,
+    "minified": 166504,
+    "gzipped": 51258
   },
   "./dist/react-big-calendar.min.js": {
-    "bundled": 464777,
-    "minified": 143849,
-    "gzipped": 45238
+    "bundled": 467470,
+    "minified": 144692,
+    "gzipped": 45468
   },
   "dist/react-big-calendar.esm.js": {
-    "bundled": 220157,
-    "minified": 99915,
-    "gzipped": 24833,
+    "bundled": 222704,
+    "minified": 100805,
+    "gzipped": 25086,
     "treeshaked": {
       "rollup": {
-        "code": 63401,
+        "code": 63734,
         "import_statements": 1445
       },
       "webpack": {
-        "code": 66894
+        "code": 67229
       }
     }
   }

package.json

@@ -95,7 +95,7 @@
     "babel-plugin-transform-rename-import": "^2.3.0",
     "babel-preset-jason": "^6.0.1",
     "bootstrap": "^3.3.5",
-    "bootstrap-sass": "^3.4.1",
+    "bootstrap-sass": "3.4.3",
     "component-metadata-loader": "^4.0.0",
     "cpy-cli": "^2.0.0",
     "eslint": "^5.8.0",

yarn.lock

@@ -3994,10 +3994,10 @@ [email protected]:
   dependencies:
     hoek "2.x.x"
 
-bootstrap-sass@^3.4.1:
-  version "3.4.1"
-  resolved "https://registry.yarnpkg.com/bootstrap-sass/-/bootstrap-sass-3.4.1.tgz#6843c73b1c258a0ac5cb2cc6f6f5285b664a8e9a"
-  integrity sha512-p5rxsK/IyEDQm2CwiHxxUi0MZZtvVFbhWmyMOt4lLkA4bujDA1TGoKT0i1FKIWiugAdP+kK8T5KMDFIKQCLYIA==
+[email protected].3:
+  version "3.4.3"
+  resolved "https://registry.yarnpkg.com/bootstrap-sass/-/bootstrap-sass-3.4.3.tgz#742cc8f4286303ae9fe8e4c95237321eae73766c"
+  integrity sha512-vPgFnGMp1jWZZupOND65WS6mkR8rxhJxndT/AcMbqcq1hHMdkcH4sMPhznLzzoHOHkSCrd6J9F8pWBriPCKP2Q==
 
 bootstrap@^3.3.5:
   version "3.4.1"