Update grammar to include new functions

Bump the grammar version from:

facetoe/grammars-v4@4a9bb0a

to include at least:

antlr/grammars-v4@259b7bb

The upstream commit includes the `present_over_time` function as well as
some other potentially useful functions.

It also includes some more changes:

- antlr/grammars-v4@f4d28d6
  - impact: duration validation
- antlr/grammars-v4@c3b0e61
  - impact: new functions
- antlr/grammars-v4@7535367
  - impact: formatting only
- antlr/grammars-v4@5660ba5
  - impact: formatting only

After regenerating the lexer and parser, I ran `black` again on the
generated files and un-did some whitespace-only changes.

Author: jadkik

Makefile

@@ -3,8 +3,8 @@ ANTLR_VERSION=4.10
 ANTLR_JAR=antlr-$(ANTLR_VERSION)-complete.jar
 
 PROJECT=grammars-v4
-GITHUB_URL=git@github.com:facetoe/$(PROJECT).git
-GRAMMAR_COMMIT=4a9bb0a5dc9cedbfafac688791ad0245a8d9d539
+GITHUB_URL=git@github.com:antlr/$(PROJECT).git
+GRAMMAR_COMMIT=3f8074f7730c272ddfd2d77df0ae83b46422fd98
 
 $(WORKDIR)/$(ANTLR_JAR):
 	mkdir -p $(WORKDIR)