Update gitpod config

- remove gitpod.Dockerfile
- set clojure as gitpod image

.gitpod.Dockerfile

@@ -1,7 +0,0 @@
-FROM clojure
-
-# Install custom tools, runtimes, etc.
-# For example "bastet", a command-line tetris clone:
-# RUN brew install bastet
-#
-# More information: https://www.gitpod.io/docs/config-docker/

.gitpod.yml

@@ -1,6 +1,5 @@
 image:
-  file: .gitpod.Dockerfile
+  file: clojure
 
 tasks:
-  - init: 'echo "TODO: Replace with init/build command"'
-    command: 'echo "TODO: Replace with command to start project"'
+  - command: 'lein koan run'