Parser stripped minus of negative numbers with unknown units (#12811)

Change-Id: I8964b1732f867cb3c5aa5859d12e94a5978adece
Merge commit '9d84c091714f01e0088fab2202c10b505e78a607'

Conflicts:
	theme-compiler/src/com/vaadin/sass/internal/parser/Parser.java

Change-Id: Ie23f14975f693c666d932d7ca1c07c980a5ba08a
Merge "Merge commit '9d84c091714f01e0088fab2202c10b505e78a607'"