fix(conflict)!: change default nav keymaps from ]x/[x to ]c/[c (#132)

## Problem

The default conflict navigation keymaps `]x`/`[x` are non-standard. Vim
natively uses `]c`/`[c` for diff navigation, so the same keys are far
more
intuitive for conflict jumping.

## Solution

Change the defaults for `conflict.keymaps.next` and
`conflict.keymaps.prev`
to `]c` and `[c`. This is a breaking change for users relying on the
previous
defaults without explicit configuration.

spec/conflict_spec.lua

@@ -12,8 +12,8 @@ local function default_config(overrides)
       theirs = 'dot',
       both = 'dob',
       none = 'don',
-      next = ']x',
-      prev = '[x',
+      next = ']c',
+      prev = '[c',
     },
   }
   if overrides then