Update backslash_escapes.rb (#431)
Update backslash_escapes.rb (#431)

Ensures that the three character octal escape, does not mistakenly match a non octal character sequence. See http://eel.is/c++draft/lex.ccon#nt:octal-escape-sequence
jeff-hykin/better-cpp-syntax,jeff-hykin/better-cpp-syntax,jeff-hykin/better-cpp-syntax,jeff-hykin/better-cpp-syntax,jeff-hykin/better-cpp-syntax,jeff-hykin/better-cpp-syntax