Update the default LTS version used

Author: Porges

stack.yaml

@@ -3,4 +3,4 @@ extra-package-dbs: []
 packages:
 - '.'
 extra-deps: []
-resolver: lts-13.4
+resolver: lts-14.7

stack.yaml.lock

@@ -0,0 +1,12 @@
+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/lock_files
+
+packages: []
+snapshots:
+- completed:
+    size: 523700
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/14/7.yaml
+    sha256: 8e3f3c894be74d71fa4bf085e0a8baae7e4d7622d07ea31a52736b80f8b9bb1a
+  original: lts-14.7