build(deps-dev): Bump gpb from 4.19.7 to 4.20.0

Bumps [gpb](https://github.com/tomas-abrahamsson/gpb) from 4.19.7 to 4.20.0.
- [Release notes](https://github.com/tomas-abrahamsson/gpb/releases)
- [Changelog](https://github.com/tomas-abrahamsson/gpb/blob/master/ChangeLog)
- [Commits](tomas-abrahamsson/gpb@4.19.7...4.20.0)

---
updated-dependencies:
- dependency-name: gpb
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

mix.lock

@@ -19,7 +19,7 @@
   "exjsx": {:hex, :exjsx, "4.0.0", "60548841e0212df401e38e63c0078ec57b33e7ea49b032c796ccad8cde794b5c", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, repo: "hexpm", optional: false]}], "hexpm"},
   "file_system": {:hex, :file_system, "0.2.10", "fb082005a9cd1711c05b5248710f8826b02d7d1784e7c3451f9c1231d4fc162d", [:mix], [], "hexpm", "41195edbfb562a593726eda3b3e8b103a309b733ad25f3d642ba49696bf715dc"},
   "gen_stage": {:hex, :gen_stage, "1.2.1", "19d8b5e9a5996d813b8245338a28246307fd8b9c99d1237de199d21efc4c76a1", [:mix], [], "hexpm", "83e8be657fa05b992ffa6ac1e3af6d57aa50aace8f691fcf696ff02f8335b001"},
-  "gpb": {:hex, :gpb, "4.19.7", "a0da133db34a62796cbffba8ae8210cc266a0e6303a79c5d92ceadc9bccc9cd0", [:make, :rebar3], [], "hexpm", "82d6a10474551b2c6d057082e05e2d7dfcfc1d22362f4bd5e9077456268d0578"},
+  "gpb": {:hex, :gpb, "4.20.0", "3617fb7762801c1bed0460ed496d5bab0f4d76e26b923a9ad9abf026c2220e8a", [:make, :rebar3], [], "hexpm", "4268756a98674d5159eeaa0fd4501b7e43b2dd7f10a1f052499e9b09f107d40b"},
   "hackney": {:hex, :hackney, "1.18.1", "f48bf88f521f2a229fc7bae88cf4f85adc9cd9bcf23b5dc8eb6a1788c662c4f6", [:rebar3], [{:certifi, "~> 2.9.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "~> 6.1.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "~> 1.0.0", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~> 1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.1", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "~> 1.1.0", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}, {:unicode_util_compat, "~> 0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a4ecdaff44297e9b5894ae499e9a070ea1888c84afdd1fd9b7b2bc384950128e"},
   "httpoison": {:hex, :httpoison, "1.8.0", "6b85dea15820b7804ef607ff78406ab449dd78bed923a49c7160e1886e987a3d", [:mix], [{:hackney, "~> 1.17", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "28089eaa98cf90c66265b6b5ad87c59a3729bea2e74e9d08f9b51eb9729b3c3a"},
   "idna": {:hex, :idna, "6.1.1", "8a63070e9f7d0c62eb9d9fcb360a7de382448200fbbd1b106cc96d3d8099df8d", [:rebar3], [{:unicode_util_compat, "~>0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "92376eb7894412ed19ac475e4a86f7b413c1b9fbb5bd16dccd57934157944cea"},