add missing externs to repo

externs/webextension_polyfill/webrequest/CertificateInfo.hx

@@ -0,0 +1,22 @@
+package webextension_polyfill.webrequest;
+
+/**
+	Contains the certificate properties of the request if it is a secure request.
+**/
+typedef CertificateInfo = {
+	var subject : String;
+	var issuer : String;
+	/**
+		Contains start and end timestamps.
+	**/
+	var validity : CertificateInfoValidityType;
+	var fingerprint : CertificateInfoFingerprintType;
+	var serialNumber : String;
+	var isBuiltInRoot : Bool;
+	var subjectPublicKeyInfoDigest : CertificateInfoSubjectPublicKeyInfoDigestType;
+	/**
+		Optional.
+	**/
+	@:optional
+	var rawDER : Array<Float>;
+};