Update xterm.js

Pulls in:

- Don't mutate options
- A null check when writing data
- Color refactor

package.json

@@ -47,7 +47,7 @@
     "vscode-nsfw": "1.0.17",
     "vscode-ripgrep": "^0.8.1",
     "vscode-textmate": "^3.3.3",
-    "vscode-xterm": "3.4.0-beta2",
+    "vscode-xterm": "3.4.0-beta3",
     "yauzl": "2.8.0"
   },
   "devDependencies": {

yarn.lock

@@ -5927,9 +5927,9 @@ vscode-textmate@^3.3.3:
     fast-plist "^0.1.2"
     oniguruma "^6.0.1"
 
-vscode-xterm@3.4.0-beta2:
-  version "3.4.0-beta2"
-  resolved "https://registry.yarnpkg.com/vscode-xterm/-/vscode-xterm-3.4.0-beta2.tgz#8800919d38c166913b4819b8524d2b3d5c05c79b"
+vscode-xterm@3.4.0-beta3:
+  version "3.4.0-beta3"
+  resolved "https://registry.yarnpkg.com/vscode-xterm/-/vscode-xterm-3.4.0-beta3.tgz#349db387bd3669ad4d6044a6ea6d699e6d649fb5"
 
 vso-node-api@^6.1.2-preview:
   version "6.1.2-preview"