Support semicolons in mixin arguments

Check https://github.com/twbs/bootstrap/commit/c017e19ed236

lesscpy/lessc/parser.py

@@ -305,6 +305,7 @@ class LessParser(object):
 
     def p_mixin_args_list_aux(self, p):
         """ mixin_args_list          : mixin_args_list ',' mixin_args
+                                     | mixin_args_list ';' mixin_args
         """
         p[1].extend([p[3]])
         p[0] = p[1]

lesscpy/test/css/mixin-args-semicolon.css

@@ -0,0 +1,3 @@
+.arguments {
+	border: 1px solid black;
+}

lesscpy/test/css/mixin-args-semicolon.min.css

@@ -0,0 +1 @@
+.arguments{border:1px solid black;}

lesscpy/test/less/mixin-args-semicolon.less

@@ -0,0 +1,6 @@
+.mixin-arguments (@width: 0px) {
+    border: @arguments;
+}
+.arguments {
+    .mixin-arguments(1px; solid; black);
+}