fix: symbols default config should not have symbols key

[steve-lorimer]

default vgit.settings.symbols config should not have a "symbols" key.

With the symbols key, after user-defined configuration is incorrectly applied

The Object:data table goes from:

data = {
  symbols = {
    void = '⣿'
  }
}

to

data = {
  symbols = {
    void = '⣿'
  },
  void = '^' -- whatever char the user defined
}

[tanvirtin]

Thanks for finding this and issuing a fix.