go-tour: add missing delete/error/rune predeclared identifier for Syntax-Highlighting

LGTM=adg
R=golang-codereviews, bradfitz, adg
CC=golang-codereviews
https://golang.org/cl/99040045
diff --git a/static/lib/codemirror/mode/go/go.js b/static/lib/codemirror/mode/go/go.js
index aa287f7..d1f989f 100644
--- a/static/lib/codemirror/mode/go/go.js
+++ b/static/lib/codemirror/mode/go/go.js
@@ -8,15 +8,15 @@
           "func":true, "go":true, "goto":true, "if":true, "import":true,
           "interface":true, "map":true, "package":true, "range":true, "return":true,
           "select":true, "struct":true, "switch":true, "type":true, "var":true,
-          "bool":true, "byte":true, "complex64":true, "complex128":true,
+          "bool":true, "byte":true, "complex64":true, "complex128":true, "error":true,
           "float32":true, "float64":true, "int8":true, "int16":true, "int32":true,
-          "int64":true, "string":true, "uint8":true, "uint16":true, "uint32":true,
+          "int64":true, "rune":true, "string":true, "uint8":true, "uint16":true, "uint32":true,
           "uint64":true, "int":true, "uint":true, "uintptr":true
         };
 
         var atoms = {
           "true":true, "false":true, "iota":true, "nil":true, "append":true,
-          "cap":true, "close":true, "complex":true, "copy":true, "imag":true,
+          "cap":true, "close":true, "complex":true, "copy":true, "delete":true, "imag":true,
           "len":true, "make":true, "new":true, "panic":true, "print":true,
           "println":true, "real":true, "recover":true
         };