Add naive and untested version of Lua language support.

testing/resources/lua_repo/.pre-commit-hooks.yaml

@@ -0,0 +1,4 @@
+-   id: hello-world-lua
+    name: hello world lua
+    entry: hello-world-lua
+    language: lua

testing/resources/lua_repo/bin/hello-world-lua

@@ -0,0 +1,3 @@
+#!/usr/bin/env lua
+
+print('hello world')

testing/resources/lua_repo/hello-dev-1.rockspec

@@ -0,0 +1,15 @@
+package = "hello"
+version = "dev-1"
+
+source = {
+   url = "git+ssh://git@github.com/pre-commit/pre-commit.git"
+}
+description = {}
+dependencies = {}
+build = {
+    type = "builtin",
+    modules = {},
+    install = {
+        bin = {"bin/hello-world-lua"}
+    },
+}