Fix num literals in YAML scalar block highlighting

[ashmaroli]

Standalone num literals in a block scalar should be tokenized as Literal::Number not Str.
However if those literals are preceded or succeeded by other non-whitespace characters, then it would be a legit Str token.
The exception is if the next tokens are whitespace and a comment:

# Mapping scalars to scalars
---
hr:  65    # Home runs
avg: 0.278 # Batting average
rbi: 147   # Runs Batted In
time: 20:03:20
staff:
  - name: Mark McGwire
    hr:   65
    avg:  0.278
    addr: B 221 Block

[pyrmont]

Just one comment from me.