Unknown instruction diagnostic parses escapes incorrectly

[rcjsuen]

FROM alpine
EXPOS\ 8080

Given the above Dockerfile, the language server will generate an error that says Unknown instruction: EXPOS080. However, the instruction is just the first word EXPOS\ so the parsing seems to be a little off here.

$ docker build .
Sending build context to Docker daemon  86.15MB
Error response from daemon: Dockerfile parse error line 2: unknown instruction: EXPOS\