drop support for Perl 5.10 and 5.12

Mojolicious's use of `length undef` throws warnings under Perl 5.10 and
causes Statocles's tests to fail. The official Mojolicious stance as of this
commit is:

> Note that Perl versions 5.10.x and 5.12.x are known to work very
> poorly with Mojolicious, and we strongly suggest you do not use them, to
> avoid stability and security issues. If it wasn't for a very vocal
> minority within the community we would not support these versions at
> all.

https://mojolicious.org/perldoc/Mojolicious/Guides/FAQ#Which-versions-of-Perl-are-supported-by-Mojolicious

Since Mojolicious is also discouraging 5.12, we might as well bump our
supported version to 5.14 (though 5.20 is where the most interesting and
useful features start appearing).

.travis.yml

@@ -1,24 +1,15 @@
 language: perl
 perl:
-    #- "5.8" # Not supported by Statocles
-    - "5.10.1" # 3-part version to ensure core-only Perl
-    - "5.12"
     - "5.14"
-    - "5.16"
-    - "5.18"
-    - "5.20"
-    - "5.22"
-    - "5.22.1" # 3-part version to ensure core-only Perl
-    - "blead"
+    - "5.26"
+    - "5.28"
 
 matrix:
     include:
-        - perl: "5.20"
+        - perl: "5.26"
           env: COVERAGE=1
-        - perl: "5.20"
+        - perl: "5.26"
           env: DEVEL_HIDE_PM="HTML::Lint::Pluggable Syntax::Highlight::Engine::Kate"
-    allow_failures:
-        - perl: "blead"
 
 before_install:
     - git clone git://github.com/travis-perl/helpers ~/travis-perl-helpers

dist.ini

@@ -117,7 +117,7 @@ allow_dirty_match = ^bin/
 ; --- Project-specific directives
 [Prereqs]
 ; Core deps
-perl = 5.010
+perl = 5.014
 strict = 0
 warnings = 0
 Encode = 0