set cwd for dlv based on program

This potentially resolves #85.

vscode-go sets dlv cwd based on the value of program.

Reference: https://github.com/golang/vscode-go/blob/master/extension/src/goDebugConfiguration.ts#L545

lua/dap-go.lua

@@ -81,6 +81,16 @@ local function setup_delve_adapter(dap, config)
   }
 
   dap.adapters.go = function(callback, client_config)
+    local program = client_config.program
+    local path = require("plenary.path")
+    local program_path = path:new(program)
+
+    if program_path:is_dir() then
+      delve_config.executable.cwd = program
+    elseif program:match("^.+(%..+)$") == ".go" then -- file extension is '.go'
+      delve_config.executable.cwd = tostring(program_path:parent())
+    end
+
     if client_config.port == nil then
       callback(delve_config)
       return