combinedef bug with a single kwarg with default value

[pablosanjose]

I believe this might be a bug:

julia> combinedef(splitdef(:((x; y=2) -> 1))) |> eval
ERROR: syntax: invalid keyword argument syntax "y = 2"
...

However if there is more than one kwargs it works

julia> combinedef(splitdef(:((x; y=2, z=2) -> 1))) |> eval
#4 (generic function with 1 method)

julia> versioninfo()
Julia Version 1.4.0
Commit b8e9a9ecc6 (2020-03-21 16:36 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin18.6.0)
  CPU: Intel(R) Core(TM) i7-8559U CPU @ 2.70GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-8.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 4
  JULIA_EDITOR = code