Fixing binop_separator="Back" for ranges

Hardcoded Separator::Place=Front in call to rewrite_pair for range
caused binop_separator="Back" to be hendled incorrectly

Fixed rewrite_pair call and the example in Configuration.md showing
the faulty behaviour

Configurations.md

@@ -341,8 +341,8 @@ fn main() {
     let sum = 123456789012345678901234567890 + 123456789012345678901234567890 +
         123456789012345678901234567890;
 
-    let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-        ..bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb; // 🐜 See #2364.
+    let range = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..
+        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb;
 }
 ```
 

src/expr.rs

@@ -250,7 +250,7 @@ fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
                         PairParts::new("", &sp_delim, ""),
                         context,
                         shape,
-                        SeparatorPlace::Front,
+                        context.config.binop_separator(),
                     )
                 }
                 (None, Some(rhs)) => {