fix hoistServerWithContext warning

copied from haskell-servant/servant#1484 (comment)

Author: peterbecich

src/Servant/API/BrowserHeader.hs

@@ -9,6 +9,7 @@
 {-# LANGUAGE ScopedTypeVariables    #-}
 {-# LANGUAGE TypeFamilies           #-}
 {-# LANGUAGE TypeOperators          #-}
+{-# LANGUAGE TypeApplications       #-}
 {-# LANGUAGE UndecidableInstances          #-}
 
 module Servant.API.BrowserHeader where
@@ -45,6 +46,9 @@ instance ( KnownSymbol sym
 
   route Proxy = route (Proxy :: Proxy (Header sym a :> sublayout))
 
+  hoistServerWithContext _ pc nt s =
+    hoistServerWithContext (Proxy @sublayout) pc nt . s
+
 
 -- Ignore BrowserHeader in HasForeign:
 instance (KnownSymbol sym, HasForeign lang ftype sublayout)