style(dune): reformat flags stanza to pass formatting check

Author: hyperpolymath

lib/dune

@@ -86,7 +86,8 @@
  ; will surface a Match_failure with file:line at runtime if exercised on an
  ; extern decl, which is the right signal for "this target has no story for
  ; host-supplied implementations".
- (flags (:standard -w -8-9))
+ (flags
+  (:standard -w -8-9))
  (preprocess
   (pps ppx_deriving.show ppx_deriving.eq ppx_deriving.ord sedlex.ppx)))