hypen-minus should be valid in sequence diagram alt/else/etc. descriptions

[gibson042]

Looking at sequenceDiagram.jison, I see that loop, opt, alt, and else all expect to be followed by actor rather than less-restrictive text (actor excludes U+002D hyphen-minus, U+003E greater-than, U+003A colon, and U+002C comma—and interestingly does not exclude U+0023 number sign).

This means that perfectly harmless descriptions are rejected, e.g.:

sequenceDiagram
    A->>B: Hello
    opt feels-like-responding
        B->>A: Hello
    end