Do not store duplicates in input history

Fixes #74.

package.json

@@ -1,6 +1,6 @@
 {
     "name": "fwdekker.com",
-    "version": "1.11.0",
+    "version": "1.11.1",
     "description": "The source code of [my personal website](https://fwdekker.com/).",
     "author": "Felix W. Dekker",
     "repository": {

src/main/js/Terminal.ts

@@ -362,7 +362,7 @@ export class InputHistory {
      * @param entry the entry to add
      */
     addEntry(entry: string): void {
-        if (entry.trim() !== "")
+        if (entry.trim() !== "" && entry.trim() !== this.history[this.history.length - 1]?.trim())
             this.history.unshift(entry);
 
         this.index = -1;