Migrate from CircleCI to GitLab CI

Motivation:

Now that the project has migrated from GitHub, it can now fully use GitLab CI.

Modifications:

Removed `circle.yml` and added `.gitlab-ci.yml` files

Result:

GitLab CI should be fully supported

.gitlab-ci.yml

@@ -0,0 +1,51 @@
+stages:
+  - build release
+  - test
+  - docs
+
+pages:
+  stage: docs
+  only:
+    - tags
+  tags:
+    - private-xcode
+  script:
+    - "echo 'TODO #45 -- Publish API Docs'"
+
+.build:
+  stage: build release
+  tags:
+    - docker
+  script:
+    - swift build -c release -v
+
+build ubuntu-xenial:
+  extends: .build
+  image: swift:5.0-xenial
+
+build ubuntu-bionic:
+  extends: .build
+  image: swift:5.0-bionic
+
+.test:
+  stage: test
+  tags:
+    - docker
+  variables:
+    REDIS_URL: 'redis'
+    REDIS_PW: 'password'
+  services:
+  - name: redis:5
+    alias: 'redis'
+    command: ["redis-server", "--requirepass", "password"]
+  script:
+    - swift build -v
+    - swift test
+
+test ubuntu-xenial:
+  extends: .test
+  image: swift:5.0-xenial
+
+test ubuntu-bionic:
+  extends: .test
+  image: swift:5.0-bionic

Tests/RedisNIOTests/Utilities/RedisConnection.swift

@@ -12,10 +12,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+import Foundation
 @testable import RedisNIO
 
 extension Redis {
     static func makeConnection() throws -> EventLoopFuture<RedisConnection> {
-        return Redis.makeConnection(to: try .init(ipAddress: "127.0.0.1", port: 6379))
+        let env = ProcessInfo.processInfo.environment
+        return Redis.makeConnection(
+            to: try .makeAddressResolvingHost(env["REDIS_URL"] ?? "127.0.0.1", port: 6379),
+            password: env["REDIS_PW"]
+        )
     }
 }

circle.yml

@@ -1,42 +0,0 @@
-version: 2
-
-jobs:
-  test-ubuntu-bionic:
-    docker:
-      - image: swift:5.0-bionic
-      - image: redis:5
-    steps:
-      - checkout
-      - run: swift build
-      - run: swift test
-  test-ubuntu-xenial:
-    docker:
-      - image: swift:5.0-xenial
-      - image: redis:5
-    steps:
-      - checkout
-      - run: swift build
-      - run: swift test
-
-  build-ubuntu-bionic:
-    docker:
-      - image: swift:5.0-bionic
-    steps:
-      - checkout
-      - run: swift build -c release
-  build-ubuntu-xenial:
-    docker:
-      - image: swift:5.0-xenial
-    steps:
-      - checkout
-      - run: swift build -c release
-workflows:
-  version: 2
-  tests:
-    jobs:
-      - test-ubuntu-bionic
-      - test-ubuntu-xenial
-  builds:
-    jobs:
-      - build-ubuntu-bionic
-      - build-ubuntu-xenial