Escape sequences have been changed in v0.7.0.
For the motivation see string literals: disallow backslash before non-escapes
Personally this change has been bugging me too (pun intended).
An easy solution is to use raw strings
julia> raw"C:\temp\some\ folder\ with\ whitespace\x.jl"
"C:\\temp\\some\\ folder\\ with\\ whitespace\\x.jl"