fix(run.lua): replace backslashes in command to prevent escape issues in insert_commented()

[PMassicotte]

There was some bad escaping in the last commit (659dc18).

Use this:

:lua require('r.run').insert_commented()

On this:

# Bad
gsub("\\d+", "X", "abc123def456")
# [1] "abc123def456"

With these changes:

# Good
gsub("\\d+", "X", "abc123def456")
# [1] "abcXdefX"

[jalvesaq]

Thank you!