Compat with upcoming JSON v1 release

[jakobnissen]

JSON.jl is about to make a huge, breaking v1 release. It would be nice if this package was compatible.

[odow]

PRs accepted

[odow]

Here's one current breaking change:

Schemas: Test Failed at /Users/oscar/.julia/dev/JSONSchema/test/runtests.jl:227
  Expression: typeof(schema.data) == Dict{String, Any}
   Evaluated: JSON.Object{String, Any} == Dict{String, Any}

Stacktrace:
 [1] macro expansion
   @ ~/.julia/juliaup/julia-1.10.10+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:672 [inlined]
 [2] macro expansion
   @ ~/.julia/dev/JSONSchema/test/runtests.jl:227 [inlined]
 [3] macro expansion
   @ ~/.julia/juliaup/julia-1.10.10+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:1577 [inlined]
 [4] top-level scope
   @ ~/.julia/dev/JSONSchema/test/runtests.jl:219
Test Summary: | Pass  Fail  Total  Time
Schemas       |    3     1      4  0.5s
ERROR: LoadError: Some tests did not pass: 3 passed, 1 failed, 0 errored, 0 broken.
in expression starting at /Users/oscar/.julia/dev/JSONSchema/test/runtests.jl:218
ERROR: Package JSONSchema errored during testing