Add cls to the list of keywords (#1038)

We have one attribute in synthetics named cls which breaks some method
calls. Let's add it to the list of keywords.

Author: therve

.generator/src/generator/formatter.py

@@ -24,6 +24,7 @@
 
 KEYWORDS = set(keyword.kwlist)
 KEYWORDS.add("property")
+KEYWORDS.add("cls")
 
 PATTERN_DOUBLE_UNDERSCORE = re.compile(r"__+")
 PATTERN_LEADING_ALPHA = re.compile(r"(.)([A-Z][a-z]+)")