Use "sourceRoot" attribute in LESS source maps to handle relative paths to source files

Author: Andrey Fedoseev

static_precompiler/compilers/less.py

@@ -67,10 +67,8 @@ def compile_file(self, source_path):
 
             # LESS, unlike SASS, can't add correct relative paths in source map when the compiled file
             # is not in the same dir as the source file. We fix it here.
-            sourcemap["sources"] = [
-                "../" * len(source_path.split("/")) + posixpath.dirname(source_path) + "/" + source
-                for source in sourcemap["sources"]
-            ]
+            sourcemap["sourceRoot"] = "../" * len(source_path.split("/")) + posixpath.dirname(source_path)
+
             sourcemap["file"] = posixpath.basename(source_path)
 
             with open(sourcemap_full_path, "w") as sourcemap_file: