Added a cargo cache to the dockerfile, so that everything isn't re-downloaded every build.

Jenkinsfile

@@ -1,5 +1,10 @@
 pipeline {
-    agent { dockerfile true }
+    agent {
+		dockerfile {
+			filename 'Dockerfile'
+			args '-v cargo-cache:/cargocache:rw -e "CARGO_HOME=/cargocache"'
+		}
+	}
     stages {
         stage('Build') {
             steps {