updating to 4.0

New design with breaking changes, gulp 4, all dependencies updated, dev environment changed, and many more changes

vendor/bootstrap/scss/mixins/_visibility.scss

@@ -0,0 +1,7 @@
+// stylelint-disable declaration-no-important
+
+// Visibility
+
+@mixin invisible($visibility) {
+  visibility: $visibility !important;
+}