Missing warning level 'suggestion' for vale

Vale can also, optionally, raise suggestions. These weren't covered yet.

autoload/ale/handlers/vale.vim

@@ -4,6 +4,8 @@
 function! ale#handlers#vale#GetType(severity) abort
     if a:severity is? 'warning'
         return 'W'
+    elseif a:severity is? 'suggestion'
+        return 'I'
     endif
 
     return 'E'

test/handler/test_vale_handler.vader

@@ -32,6 +32,14 @@ Execute(The vale handler should handle a normal example):
   \     'text': "'Documentation' is repeated!",
   \     'code': 'vale.Repetition',
   \   },
+  \   {
+  \     'lnum': 7,
+  \     'col': 1,
+  \     'end_col': 27,
+  \     'type': 'I',
+  \     'text': "'Documentation' is repeated!",
+  \     'code': 'vale.Repetition',
+  \   },
   \ ],
   \ ale#handlers#vale#Handle(bufnr(''), [
   \   '{',
@@ -61,6 +69,19 @@ Execute(The vale handler should handle a normal example):
   \   '        27',
   \   '      ],',
   \   '      "Hide": false',
+  \   '    },',
+  \   '    {',
+  \   '      "Check": "vale.Repetition",',
+  \   '      "Description": "",',
+  \   '      "Line": 7,',
+  \   '      "Link": "",',
+  \   "      \"Message\": \"'Documentation' is repeated!\",",
+  \   '      "Severity": "suggestion",',
+  \   '      "Span": [',
+  \   '        1,',
+  \   '        27',
+  \   '      ],',
+  \   '      "Hide": false',
   \   '    }',
   \   '  ]',
   \   '}',