update bootstrap 4.3.1, update gulpfile, npm start script added, change SCSS file names for proper compiling

vendor/bootstrap/scss/_dropdown.scss

@@ -7,6 +7,8 @@
 }
 
 .dropdown-toggle {
+  white-space: nowrap;
+
   // Generate the caret automatically
   @include caret;
 }
@@ -22,8 +24,8 @@
   min-width: $dropdown-min-width;
   padding: $dropdown-padding-y 0;
   margin: $dropdown-spacer 0 0; // override default ul
-  font-size: $font-size-base; // Redeclare because nesting can cause inheritance issues
-  color: $body-color;
+  @include font-size($dropdown-font-size);
+  color: $dropdown-color;
   text-align: left; // Ensures proper alignment if parent has it changed (e.g., modal footer)
   list-style: none;
   background-color: $dropdown-bg;
@@ -33,17 +35,6 @@
   @include box-shadow($dropdown-box-shadow);
 }
 
-@each $breakpoint in map-keys($grid-breakpoints) {
-  @include media-breakpoint-up($breakpoint) {
-    $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
-
-    .dropdown-menu#{$infix}-right {
-      right: 0;
-      left: auto;
-    }
-  }
-}
-
 @each $breakpoint in map-keys($grid-breakpoints) {
   @include media-breakpoint-up($breakpoint) {
     $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
@@ -52,6 +43,11 @@
       right: auto;
       left: 0;
     }
+
+    .dropdown-menu#{$infix}-right {
+      right: 0;
+      left: auto;
+    }
   }
 }
 
@@ -118,7 +114,7 @@
 
 // Dividers (basically an `<hr>`) within the dropdown
 .dropdown-divider {
-  @include nav-divider($dropdown-divider-bg);
+  @include nav-divider($dropdown-divider-bg, $dropdown-divider-margin-y);
 }
 
 // Links, buttons, and more within the dropdown menu
@@ -136,12 +132,16 @@
   background-color: transparent; // For `<button>`s
   border: 0; // For `<button>`s
 
-  &:first-child {
-    @include border-top-radius($dropdown-inner-border-radius);
-  }
+  // Prevent dropdown overflow if there's no padding
+  // See https://github.com/twbs/bootstrap/pull/27703
+  @if $dropdown-padding-y == 0 {
+    &:first-child {
+      @include border-top-radius($dropdown-inner-border-radius);
+    }
 
-  &:last-child {
-    @include border-bottom-radius($dropdown-inner-border-radius);
+    &:last-child {
+      @include border-bottom-radius($dropdown-inner-border-radius);
+    }
   }
 
   @include hover-focus {
@@ -178,7 +178,7 @@
   display: block;
   padding: $dropdown-padding-y $dropdown-item-padding-x;
   margin-bottom: 0; // for use with heading elements
-  font-size: $font-size-sm;
+  @include font-size($font-size-sm);
   color: $dropdown-header-color;
   white-space: nowrap; // as with > li > a
 }