Manage development dependencies better.

New version of Rubygems complains about version quantifiers being
otherwise a little bit too lax.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Fix issues reported by clang.

This concerns the following:

  In file included from ../../../../ext/fizzbuzz/fizzbuzz.c:21:
  ../../../../ext/fizzbuzz/fizzbuzz.h:106:8: error: redefinition of 'exception'
  struct exception {
        ^
  /usr/include/math.h:637:8: note: previous definition is here
  struct exception {
        ^

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>