fix call site and now seperated assignment (was bunged as operator)

test/cases/assignment/assignment_instance.tst

@@ -1,6 +1,9 @@
-a = 5
+self.a = 5
 -- -- --
-s(:expressions, 
-  s(:assign, 
-    s(:name,  :a), 
-    s(:int,  5)))
+s(:assignment,
+  s(:field_access,
+    s(:receiver,
+      s(:name, :self)),
+    s(:field,
+      s(:name, :a))),
+  s(:int, 5))

test/cases/assignment/name.tst

@@ -0,0 +1,5 @@
+name = 10
+-- -- --
+s(:assignment,
+  s(:name, :name),
+  s(:int, 10))