handle end of file

Closes #1

grammar.js

@@ -36,7 +36,7 @@ module.exports = grammar({
             $.container,
             $.connection
           ),
-          $._end
+          choice($._end, "\0")
         )
       ),
 

src/grammar.json

@@ -46,8 +46,13 @@
               ]
             },
             {
-              "type": "SYMBOL",
-              "name": "_end"
+              "type": "CHOICE",
+              "members": [
+                {
+                  "type": "SYMBOL",
+                  "name": "_end"
+                }
+              ]
             }
           ]
         }

test/corpus/shape.txt

@@ -1,3 +1,13 @@
+================================================================================
+Handle end of file (issue #1)
+================================================================================
+foo
+--------------------------------------------------------------------------------
+
+(source_file
+  (shape (shape_key))
+)
+
 ================================================================================
 Simple shape key
 ================================================================================