Fix location of MacroExpression nodes

[Sija]

Fixes incorrect location of MacroExpression nodes, due to the fact that:

1. @token.location was being called too late, since parse_macro_expression was advancing the position before the assignment
2. and OTOH token_end_location was being called too early

Before this PR:

node         # => {{ type }}
location     # => src/random.cr:320:45
end_location # => src/random.cr:320:45

source_between(location, end_location) # => "}"

after:

node         # => {{ type }}
location     # => src/random.cr:320:39
end_location # => src/random.cr:320:46

source_between(location, end_location) # => "{{type}}"