Revert "Revert "Re-enable doctest suites""

This reverts commit a10011824d.

build-constraints.yaml

@@ -2774,10 +2774,6 @@ package-flags:
     tar:
         old-time: false
 
-    # https://github.com/fpco/stackage/pull/482#issuecomment-83635207
-    jose-jwt:
-        doctest: false
-
     time-locale-compat:
         old-locale: false
 
@@ -3080,12 +3076,6 @@ expected-test-failures:
     - distributed-process-supervisor # # https://github.com/haskell-d
     - ghcid # Weird conflicts with sandboxingistributed/distributed-process-supervisor/issues/1
 
-    # Doctest ran across ambiguous modules
-    # https://github.com/bergmark/blog/blob/master/2016/package-faq.md#ambiguous-modules-when-using-doctest
-    - doctest # 0.11.0 https://github.com/sol/doctest/issues/137
-    - jwt # https://bitbucket.org/ssaasen/haskell-jwt/issues/18/test-suite-build-failure-in-stackage
-    - warp # https://github.com/yesodweb/wai/issues/579
-
     # Stackage upper bounds, re-enable these when their upper bound is removed
     - hindent # 4.6.4