Add fixer for Go modules (#1873)

* Add fixer for Go modules

autoload/ale/fix/registry.vim

@@ -145,6 +145,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['go'],
 \       'description': 'Fix Go files imports with goimports.',
 \   },
+\   'gomod': {
+\       'function': 'ale#fixers#gomod#Fix',
+\       'suggested_filetypes': ['gomod'],
+\       'description': 'Fix Go module files with go mod edit -fmt.',
+\   },
 \   'tslint': {
 \       'function': 'ale#fixers#tslint#Fix',
 \       'suggested_filetypes': ['typescript'],