chore(deps): update dependency flow to v1.2.4

mix.lock

@@ -9,8 +9,8 @@
   "excoveralls": {:hex, :excoveralls, "0.14.6", "610e921e25b180a8538229ef547957f7e04bd3d3e9a55c7c5b7d24354abbba70", [:mix], [{:hackney, "~> 1.16", [hex: :hackney, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "0eceddaa9785cfcefbf3cd37812705f9d8ad34a758e513bb975b081dce4eb11e"},
   "exjsx": {:hex, :exjsx, "4.0.0", "60548841e0212df401e38e63c0078ec57b33e7ea49b032c796ccad8cde794b5c", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, repo: "hexpm", optional: false]}], "hexpm", "32e95820a97cffea67830e91514a2ad53b888850442d6d395f53a1ac60c82e07"},
   "exvcr": {:hex, :exvcr, "0.11.1", "a5e5f57a67538e032e16cfea6cfb1232314fb146e3ceedf1cde4a11f12fb7a58", [:mix], [{:exactor, "~> 2.2", [hex: :exactor, repo: "hexpm", optional: false]}, {:exjsx, "~> 4.0", [hex: :exjsx, repo: "hexpm", optional: false]}, {:httpoison, "~> 1.0", [hex: :httpoison, repo: "hexpm", optional: true]}, {:httpotion, "~> 3.1", [hex: :httpotion, repo: "hexpm", optional: true]}, {:ibrowse, "~> 4.4", [hex: :ibrowse, repo: "hexpm", optional: true]}, {:meck, "~> 0.8", [hex: :meck, repo: "hexpm", optional: false]}], "hexpm", "984a4d52d9e01d5f0e28d45718565a41dffab3ac18e029ae45d42f16a2a58a1d"},
-  "flow": {:hex, :flow, "1.2.0", "515e03aa3d056cecc3e3f1e80f6ca4bbf5f45b13c88dee5db880b2f3f24f1caa", [:mix], [{:gen_stage, "~> 1.0", [hex: :gen_stage, repo: "hexpm", optional: false]}], "hexpm", "1b45bfc8a9202c5ec80b077c21df133561e56c56189ba4082dddccb6b5762525"},
-  "gen_stage": {:hex, :gen_stage, "1.1.2", "b1656cd4ba431ed02c5656fe10cb5423820847113a07218da68eae5d6a260c23", [:mix], [], "hexpm", "9e39af23140f704e2b07a3e29d8f05fd21c2aaf4088ff43cb82be4b9e3148d02"},
+  "flow": {:hex, :flow, "1.2.4", "1dd58918287eb286656008777cb32714b5123d3855956f29aa141ebae456922d", [:mix], [{:gen_stage, "~> 1.0", [hex: :gen_stage, repo: "hexpm", optional: false]}], "hexpm", "874adde96368e71870f3510b91e35bc31652291858c86c0e75359cbdd35eb211"},
+  "gen_stage": {:hex, :gen_stage, "1.2.1", "19d8b5e9a5996d813b8245338a28246307fd8b9c99d1237de199d21efc4c76a1", [:mix], [], "hexpm", "83e8be657fa05b992ffa6ac1e3af6d57aa50aace8f691fcf696ff02f8335b001"},
   "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"},