Build failure with GHC 8.4

Add semigroup instances. See also: https://ghc.haskell.org/trac/ghc/wiki/Migration/8.4#SemigroupMonoidsuperclasses

Building library for tinylog-0.14.0..
[1 of 4] Compiling System.Logger.Message ( src/System/Logger/Message.hs, dist/bu
ild/System/Logger/Message.o )

src/System/Logger/Message.hs:52:10: error:
    • No instance for (Semigroup Builder)
        arising from the superclasses of an instance declaration
      There are instances for similar types:
        instance Semigroup B.Builder
          -- Defined in ‘Data.ByteString.Builder.Internal’
    • In the instance declaration for ‘Monoid Builder’
   |
52 | instance Monoid Builder where
   |          ^^^^^^^^^^^^^^

src/System/Logger/Message.hs:126:11: error:
    • Could not deduce (Semigroup Builder) arising from a use of ‘<>’
      from the context: (ToBytes a, ToBytes b)
        bound by the type signature for:
                   (+++) :: forall a b. (ToBytes a, ToBytes b) => a -> b -> Builder
        at src/System/Logger/Message.hs:125:1-52
      There are instances for similar types:
        instance Semigroup B.Builder
          -- Defined in ‘Data.ByteString.Builder.Internal’
    • In the expression: bytes a <> bytes b
      In an equation for ‘+++’: a +++ b = bytes a <> bytes b
    |
126 | a +++ b = bytes a <> bytes b
    |           ^^^^^^^^^^^^^^^^^^