use env vars to determine the docker API version (closes #71)

README.md

@@ -88,7 +88,6 @@ When running you'll need to include the docker client binary and socket file:
 ```bash
 docker run --rm -it \
     -v /var/run/docker.sock:/var/run/docker.sock \
-    -v $(which docker):/bin/docker \
     wagoodman/dive:latest <dive arguments...>
 ```
 
@@ -96,7 +95,18 @@ Docker for Windows (showing PowerShell compatible line breaks; collapse to a sin
 ```bash
 docker run --rm -it `
     -v /var/run/docker.sock:/var/run/docker.sock `
-    -v /usr/local/bin/docker:/bin/docker `
+    wagoodman/dive:latest <dive arguments...>
+```
+
+**Note:** depending on the version of docker you are running locally you may need to specify the docker API version as an environment variable:
+```bash
+   DOCKER_API_VERSION=1.37 dive ...
+``` 
+or if you are running with a docker image:
+```bash
+docker run --rm -it \
+    -v /var/run/docker.sock:/var/run/docker.sock \
+    -e DOCKER_API_VERSION=1.37
     wagoodman/dive:latest <dive arguments...>
 ```
 

image/image.go

@@ -199,12 +199,10 @@ func InitializeData(imageID string) ([]*Layer, []*filetree.FileTree, float64, fi
 	var manifest ImageManifest
 	var layerMap = make(map[string]*filetree.FileTree)
 	var trees = make([]*filetree.FileTree, 0)
-	dockerVersion = utils.DiscoverDockerVersion()
-	logrus.Debug("Using docker version:", dockerVersion)
 
 	// pull the image if it does not exist
 	ctx := context.Background()
-	dockerClient, err := client.NewClientWithOpts(client.WithVersion(dockerVersion), client.FromEnv)
+	dockerClient, err := client.NewClientWithOpts(client.FromEnv)
 	if err != nil {
 		fmt.Println("Could not connect to the Docker daemon:" + err.Error())
 		utils.Exit(1)

utils/docker.go

@@ -1,7 +1,6 @@
 package utils
 
 import (
-	"bytes"
 	"os"
 	"os/exec"
 	"strings"
@@ -31,15 +30,3 @@ func cleanArgs(s []string) []string {
 	}
 	return r
 }
-
-func DiscoverDockerVersion() string {
-	cmd := exec.Command("docker", "version", "--format", "{{.Server.APIVersion}}")
-	cmdOutput := &bytes.Buffer{}
-	cmd.Stdout = cmdOutput
-
-	err := cmd.Run()
-	if err != nil {
-		panic(err)
-	}
-	return strings.TrimSpace(string(cmdOutput.Bytes()))
-}