chore: drop python 3.6 and update ujson (#190)

* chore: depreciate python 3.6 support & upate ujson

after collection python version info metrics, we fount that only 2 users
are still using python 3.6. since it has been eol for 5 months now,
we believe it's safe to let it go.

rest easy 3.6 ⚰✨- you served us well 🫡

closes Please upgrade the ujson dependency, which has a CVE #160

* chore: upgrade and clean some deps

.circleci/config.yml

@@ -65,7 +65,7 @@ workflows:
       - test:
           matrix:
             parameters:
-              tag: ["3.6", "3.7", "3.8", "3.9"]
+              tag: ["3.7", "3.8", "3.9", "3.10"]
           filters:
             tags:
               only: /.*/

pyproject.toml

@@ -11,11 +11,11 @@ homepage = "https://speckle.systems/"
 
 
 [tool.poetry.dependencies]
-python = "^3.6.5"
+python = ">=3.7.0, <4.0"
 pydantic = "^1.8.2"
 appdirs = "^1.4.4"
 gql = {extras = ["requests", "websockets"], version = "^3.3.0"}
-ujson = "^4.3.0"
+ujson = "^5.3.0"
 Deprecated = "^1.2.13"
 
 [tool.poetry.dev-dependencies]