Update CMUdict with more recent 0.7b entries
Signed-off-by: Jocelyn Huang <jocelynh@nvidia.com>

# What does this PR do ?

Merges the existing NeMo CMUdict with a version of 0.7b with added entries.

**Collection**: TTS

# Changelog 
- Added entries from https://github.com/Alexir/CMUdict/blob/master/cmudict-0.7b
- I've omitted entries with British spellings