Switch to pre-1.8 version of tzdata.

tzdata 1.0.0 requires Elixir 1.8.0, but we target 1.7. Fortunately
tzdata issues bugfix releases for pre-1.8.0 version.

mix.exs

@@ -95,7 +95,7 @@ defp oauth_deps do
   defp deps do
     [
       {:phoenix, "~> 1.4.8"},
-      {:tzdata, "~> 1.0"},
+      {:tzdata, "~> 0.5.21"},
       {:plug_cowboy, "~> 2.0"},
       {:phoenix_pubsub, "~> 1.1"},
       {:phoenix_ecto, "~> 4.0"},

mix.lock

@@ -87,7 +87,7 @@
   "tesla": {:hex, :tesla, "1.2.1", "864783cc27f71dd8c8969163704752476cec0f3a51eb3b06393b3971dc9733ff", [:mix], [{:exjsx, ">= 3.0.0", [hex: :exjsx, repo: "hexpm", optional: true]}, {:fuse, "~> 2.4", [hex: :fuse, repo: "hexpm", optional: true]}, {:hackney, "~> 1.6", [hex: :hackney, repo: "hexpm", optional: true]}, {:ibrowse, "~> 4.4.0", [hex: :ibrowse, repo: "hexpm", optional: true]}, {:jason, ">= 1.0.0", [hex: :jason, repo: "hexpm", optional: true]}, {:mime, "~> 1.0", [hex: :mime, repo: "hexpm", optional: false]}, {:poison, ">= 1.0.0", [hex: :poison, repo: "hexpm", optional: true]}], "hexpm"},
   "timex": {:hex, :timex, "3.6.1", "efdf56d0e67a6b956cc57774353b0329c8ab7726766a11547e529357ffdc1d56", [:mix], [{:combine, "~> 0.10", [hex: :combine, repo: "hexpm", optional: false]}, {:gettext, "~> 0.10", [hex: :gettext, repo: "hexpm", optional: false]}, {:tzdata, "~> 0.1.8 or ~> 0.5 or ~> 1.0.0", [hex: :tzdata, repo: "hexpm", optional: false]}], "hexpm"},
   "trailing_format_plug": {:hex, :trailing_format_plug, "0.0.7", "64b877f912cf7273bed03379936df39894149e35137ac9509117e59866e10e45", [:mix], [{:plug, "> 0.12.0", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
-  "tzdata": {:hex, :tzdata, "1.0.1", "f6027a331af7d837471248e62733c6ebee86a72e57c613aa071ebb1f750fc71a", [:mix], [{:hackney, "~> 1.0", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm"},
+  "tzdata": {:hex, :tzdata, "0.5.21", "8cbf3607fcce69636c672d5be2bbb08687fe26639a62bdcc283d267277db7cf0", [:mix], [{:hackney, "~> 1.0", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm"},
   "ueberauth": {:hex, :ueberauth, "0.6.1", "9e90d3337dddf38b1ca2753aca9b1e53d8a52b890191cdc55240247c89230412", [:mix], [{:plug, "~> 1.5", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.4.1", "d869e4c68901dd9531385bb0c8c40444ebf624e60b6962d95952775cac5e90cd", [:rebar3], [], "hexpm"},
   "unsafe": {:hex, :unsafe, "1.0.1", "a27e1874f72ee49312e0a9ec2e0b27924214a05e3ddac90e91727bc76f8613d8", [:mix], [], "hexpm"},