Add Instantations to Grammar

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

tree-sitter-p4/test/corpus/transitions.txt

@@ -29,8 +29,8 @@ parser simple() {
     )
    )
   )
-  (semicolon)
  )
+ (semicolon)
 )
 
 =========================
@@ -83,6 +83,6 @@ parser simple() {
     )
    )
   )
-  (semicolon)
  )
+ (semicolon)
 )