remove blead from travis build

complains about:

	Installing the dependencies failed:
		Installed version (7.04_01) of ExtUtils::MakeMaker
		is not in range '7.0401'

which is obviously nonsense but i'm not interested in investigating
this at present and assume it will fix itself eventually (at which
point i will add 5.22 to the .travis file)

.travis.yml

@@ -1,6 +1,5 @@
 language: perl
 perl:
-    - "blead"
     - "5.20"
     - "5.18"
     - "5.16"