Add Dockerfile to support running in a container

Dockerfile

@@ -0,0 +1,41 @@
+# To build:
+#
+#   docker build -t repolinter .
+#
+# To run against the current directory:
+#
+#   docker run -t -v $PWD:/src repolinter
+#
+# To run against a remote GitHub repository
+#
+#   docker run -t repolinter --git https://github.com/username/repo.git
+#
+FROM ruby:2.5.1-slim as ruby-deps
+
+ENV RUNTIME_DEPS git
+ENV BUILD_DEPS make build-essential cmake pkg-config libicu-dev zlib1g-dev libcurl4-openssl-dev libssl-dev
+
+RUN apt-get update && \
+    apt-get install --no-install-recommends -y $RUNTIME_DEPS $BUILD_DEPS && \
+    gem install --no-document licensee github-linguist && \
+    apt-get remove -y $BUILD_DEPS && \
+    apt-get autoremove -y && \
+    rm -rf /var/lib/apt/lists/*
+
+
+FROM node:10-slim
+
+# Copy Ruby dependencies
+COPY --from=ruby-deps . .
+
+# Copy ENV from Ruby image
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+
+WORKDIR /app
+COPY package*.json ./
+RUN npm install --production
+COPY . .
+
+ENTRYPOINT ["node", "/app/bin/repolinter.js"]

lib/linguist.js

@@ -11,12 +11,15 @@ class Linguist {
    * Throws 'Linguist not installed' error if command line of 'linguist' is not available.
    */
   identifyLanguagesSync (targetDir) {
-    const linguistOutput = spawnSync('linguist', [targetDir, '--json']).stdout
-    if (linguistOutput == null) {
-      throw new Error('Linguist not installed')
+    // Command was renamed in https://github.com/github/linguist/pull/4208
+    for (const command of ['github-linguist', 'linguist']) {
+      const output = spawnSync(command, [targetDir, '--json']).stdout
+      if (output !== null) {
+        return JSON.parse(output.toString())
+      }
     }
-    const json = linguistOutput.toString()
-    return JSON.parse(json)
+
+    throw new Error('Linguist not installed')
   }
 }