tools: use default resolver for Shake and hakyll-std again

Shake.hs

@@ -1,7 +1,6 @@
 #!/usr/bin/env stack
 {- stack exec
    --verbosity=info
-   --stack-yaml=stack-ghc8.2.yaml
    --package base-prelude
    --package directory
    --package extra

site/hakyll-std/hakyll-std.hs

@@ -1,6 +1,5 @@
 #!/usr/bin/env stack
 {- stack exec --verbosity info
-   --stack-yaml=../../stack-ghc8.2.yaml
    --package hakyll
    ghc
 -}