message: Fix spelling error chache -> cache.
diff: # Bitcoin Core GitHub member via the Travis web interface [0].
  #
  # Travis CI uploads the cache after the script phase of the build [1].
  -# However, the build is terminated without saving the chache if it takes over
  +# However, the build is terminated without saving the cache if it takes over
  # 50 minutes [2]. Thus, if we spent too much time in early build stages, fail
  # with an error and save the cache.
  #
  