Bump excon from 0.67.0 to 0.71.0 for ci on mac & linux (#48268)

diff --git a/dev/ci/docker_linux/Dockerfile b/dev/ci/docker_linux/Dockerfile
index 551b630..6a3fe89 100644
--- a/dev/ci/docker_linux/Dockerfile
+++ b/dev/ci/docker_linux/Dockerfile
@@ -127,6 +127,7 @@
 # Skip all the documentation (-N) since it's just on CI.
 RUN gem install bundler -N
 
+# Gemfile last edited 1/6/2019 (update to trigger a rebuild of Docker image)
 COPY Gemfile /Gemfile
 COPY Gemfile.lock /Gemfile.lock
 
diff --git a/dev/ci/docker_linux/Gemfile b/dev/ci/docker_linux/Gemfile
index 9b041f8..9fdb92a 100644
--- a/dev/ci/docker_linux/Gemfile
+++ b/dev/ci/docker_linux/Gemfile
@@ -1,3 +1,6 @@
+# When editing this file, update the comment starting "# Gemfile last edited"
+# in dev/ci/docker_linux/Dockerfile to retrigger a Docker build on Cirrus.
+
 source "https://rubygems.org"
 
 # Install fastlane which is used on Linux to build and deploy Android
diff --git a/dev/ci/docker_linux/Gemfile.lock b/dev/ci/docker_linux/Gemfile.lock
index b3085a2..f21f85d 100644
--- a/dev/ci/docker_linux/Gemfile.lock
+++ b/dev/ci/docker_linux/Gemfile.lock
@@ -18,7 +18,7 @@
       unf (>= 0.0.5, < 1.0.0)
     dotenv (2.7.5)
     emoji_regex (1.0.1)
-    excon (0.67.0)
+    excon (0.71.0)
     faraday (0.17.0)
       multipart-post (>= 1.2, < 3)
     faraday-cookie_jar (0.0.6)
@@ -153,7 +153,7 @@
   ruby
 
 DEPENDENCIES
-  fastlane
+  fastlane (= 2.134.0)
 
 BUNDLED WITH
   2.0.2