Rename base/strings/utf8proc.jl to base/strings/unicode.jl

To match the new name of the module.

Author: nalimilan

base/strings/strings.jl

@@ -4,6 +4,6 @@ include("strings/errors.jl")
 include("strings/substring.jl")
 include("strings/basic.jl")
 include("strings/search.jl")
-include("strings/utf8proc.jl")
+include("strings/unicode.jl")
 include("strings/util.jl")
 include("strings/io.jl")