repair slightly damaged source file
The source file db/pipeline/expression.cpp had somehow come to have a line ending in CR CR LF, which prevented Git's autocrlf feature from converting between Windows CRLF mode and Unix LF mode. It also breaks the Google Code Review process, which chokes on the file. So, just convert the file to Unix line endings and re-upload it. It may look like nothing changed or every line changed, but it's just the line endings, no functional change.