Be consistent with Popper's name. (#32224)

The npm package is named "popper.js" but the project is named "Popper", so use the latter consistently.

js/src/dropdown.js

@@ -156,10 +156,10 @@ class Dropdown {
       return
     }
 
-    // Disable totally Popper.js for Dropdown in Navbar
+    // Totally disable Popper for Dropdowns in Navbar
     if (!this._inNavbar) {
       if (typeof Popper === 'undefined') {
-        throw new TypeError('Bootstrap\'s dropdowns require Popper.js (https://popper.js.org)')
+        throw new TypeError('Bootstrap\'s dropdowns require Popper (https://popper.js.org)')
       }
 
       let referenceElement = this._element
@@ -329,7 +329,7 @@ class Dropdown {
       }
     }
 
-    // Disable Popper.js if we have a static display
+    // Disable Popper if we have a static display
     if (this._config.display === 'static') {
       popperConfig.modifiers.applyStyle = {
         enabled: false

js/src/tooltip.js

@@ -125,7 +125,7 @@ const TRIGGER_MANUAL = 'manual'
 class Tooltip {
   constructor(element, config) {
     if (typeof Popper === 'undefined') {
-      throw new TypeError('Bootstrap\'s tooltips require Popper.js (https://popper.js.org)')
+      throw new TypeError('Bootstrap\'s tooltips require Popper (https://popper.js.org)')
     }
 
     // private