Fix syntax coloring in string interpolation

Start the match just before the \( part

Author: Akshay Hegde

syntax/swift.vim

@@ -54,7 +54,7 @@ delfunction s:CommentKeywordMatch
 " Literals
 " Strings
 syntax region swiftString start=/"/ skip=/\\\\\|\\"/ end=/"/ contains=swiftInterpolatedWrapper oneline
-syntax region swiftInterpolatedWrapper start="\v[^\\]\\\(\s*" end="\v\s*\)" contained containedin=swiftString contains=swiftInterpolatedString,swiftString oneline
+syntax region swiftInterpolatedWrapper start="\v[^\\]\zs\\\(\s*" end="\v\s*\)" contained containedin=swiftString contains=swiftInterpolatedString,swiftString oneline
 syntax match swiftInterpolatedString "\v\w+(\(\))?" contained containedin=swiftInterpolatedWrapper oneline
 
 " Numbers