[skip changelog] Use local path for github.com/arduino/arduino-cli module dependency of docsgen (#719)

Previously, docsgen used a pinned version of the github.com/arduino/arduino-cli module, which resulted in the generated command documentation not reflecting updates to the Arduino CLI command line interface made after the pinned version.

The new approach is to use the current version of the module from the local path, resulting in the generated documentation always matching the associated version of Arduino CLI.

(cherry picked from commit 8220b32)

Author: per1234

docsgen/go.mod

@@ -2,7 +2,9 @@ module github.com/arduino/arduino-cli/docsgen
 
 go 1.14
 
+replace github.com/arduino/arduino-cli => ../
+
 require (
-	github.com/arduino/arduino-cli v0.0.0-20200228161349-4b874a02b096
+	github.com/arduino/arduino-cli v0.0.0
 	github.com/spf13/cobra v0.0.6
 )