Make maze specs a bit cleaner/more communicative.
Make path specs a bit cleaner/more communicative.
Clean up a -w warning.
Store maze as a 2-D array for performance.

Maze solving is 3x-4x faster with this change.
Clean up row and cell access.
Move the maze class down to lib with a top-level maze.rb to require it.

Ideally, the project would be named differently than the main class.