OpenFeignGH-1246: Initial Circle CI Configuration (OpenFeign#1331)

This change includes our initial Circle CI configuration.

.circleci/config.yml

@@ -0,0 +1,35 @@
+# Java Maven CircleCI 2.0 configuration file
+#
+# Check https://circleci.com/docs/2.0/language-java/ for more details
+#
+
+# our job defaults
+defaults: &defaults
+  docker:
+    - image: circleci/openjdk:11.0.8
+  working_directory: ~/feign
+  environment:
+    # Customize the JVM maximum heap limit
+    MAVEN_OPTS: -Xmx3200m
+
+version: 2.1
+jobs:
+  build:
+    <<: *defaults
+    steps:
+      - checkout
+      - restore_cache:
+          keys:
+            - feign-dependencies-{{ checksum "pom.xml" }}
+            - feign-dependencies-
+      - run: mvn dependency:resolve-plugins go-offline:resolve-dependencies install -DskipTests=true
+      - save_cache:
+          paths:
+            - ~/.m2
+          key: feign-dependencies-{{ checksum "pom.xml" }}
+      - run: mvn -o test
+workflows:
+  version: 2
+  build:
+    jobs:
+      - build