update Hakyll

[cblp]

/Users/cblp/dev/ruhaskell/src/Markup/About.hs:15:17: error: [-Wdeprecations, -Werror=deprecations]
    In the use of ‘readTemplate’
    (imported from Hakyll.Web.Template, but defined in Hakyll.Web.Template.Internal):
    Deprecated: "Use templateCompiler instead"
   |
15 | aboutTemplate = readTemplate . Text.unpack . renderHtml $ raw
   |                 ^^^^^^^^^^^^

It's better to update Hakyll along with the stack resolver to lts-16.31.

Where to start:

--- a/stack.yaml
+++ b/stack.yaml
@@ -1,8 +1,4 @@
-resolver: lts-14.0
-
-extra-deps:
-  - hakyll-4.12.5.2
-  # TODO - hakyll-4.13.0.0
+resolver: lts-16.31
 
 flags:
   hakyll:

[cblp]

fixed