internal/lsp: use interface for diagnostics code

Since the diagnostics code can be either a string or a number, use an
empty interface.

Change-Id: Ie1a4183b5c82ef177176075828511070ae3520bd
Reviewed-on: https://go-review.googlesource.com/c/161217
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/internal/lsp/protocol/basic.go b/internal/lsp/protocol/basic.go
index 0dd2f5e..a8bd96c 100644
--- a/internal/lsp/protocol/basic.go
+++ b/internal/lsp/protocol/basic.go
@@ -106,7 +106,7 @@
 	/**
 	 * The diagnostic's code, which might appear in the user interface.
 	 */
-	Code string `json:"code,omitempty"` // number | string
+	Code interface{} `json:"code,omitempty"` // number | string
 
 	/**
 	 * A human-readable string describing the source of this