Fix protocol.json ("true" => true), as introduced in r146349.

Source/devtools/protocol.json

Index: Source/devtools/protocol.json
diff --git a/Source/devtools/protocol.json b/Source/devtools/protocol.json
index 024e7b06dcc02eb7178292d78b58e2f28cb1ba4f..20721f8de333501944d41cabea2e2010500a3142 100644
--- a/Source/devtools/protocol.json
+++ b/Source/devtools/protocol.json
@@ -453,7 +453,7 @@
                 "description": "Accepts or dismisses a JavaScript initiated dialog (alert, confirm, prompt, or onbeforeunload).",
                 "parameters": [
                     { "name": "accept", "type": "boolean", "description": "Whether to accept or dismiss the dialog." },
-                    { "name": "promptText", "type": "string", "optional": "true", "description": "The text to enter into the dialog prompt before accepting. Used only if this is a prompt dialog." }
+                    { "name": "promptText", "type": "string", "optional": true, "description": "The text to enter into the dialog prompt before accepting. Used only if this is a prompt dialog." }
                 ],
                 "hidden": true
             }