Update bounds for GHC 8.10

[robx]

swagger2 currently doesn't build with GHC 8.10 (was checking PostgREST dependencies).

It turns out we'll have to wait for a new optics release well-typed/optics#297 since optics 0.2 properly doesn't build with GHC currently, but I thought I'd log the progress I've made so far:

With this diff to swagger2.cabal

--- a/swagger2.cabal
+++ b/swagger2.cabal
@@ -60,10 +60,10 @@ library
 
   -- GHC boot libraries
   build-depends:
-      base             >=4.9      && <4.14
+      base             >=4.9      && <4.15
     , bytestring       >=0.10.4.0 && <0.11
     , containers       >=0.5.5.1  && <0.7
-    , template-haskell >=2.9.0.0  && <2.16
+    , template-haskell >=2.9.0.0  && <2.17
     , time             >=1.4.2    && <1.10
     , transformers     >=0.3.0.0  && <0.6
 
@@ -82,7 +82,7 @@ library
     , hashable                  >=1.2.7.0  && <1.4
     , http-media                >=0.7.1.2  && <0.9
     , insert-ordered-containers >=0.2.3    && <0.3
-    , lens                      >=4.16.1   && <4.19
+    , lens                      >=4.16.1   && <4.20
     , network                   >=2.6.3.5  && <3.2
     , optics-core               >=0.2      && <0.3
     , optics-th                 >=0.2      && <0.3

the package can be configured successfully with

cabal configure --enable-tests --allow-newer=template-haskell --allow-newer=base --allow-newer=lens

(but the build fails when trying to compile optics). I expect that by additionally relaxing the optics bounds to allow 0.4, this should be enough.