[requirements.txt] change fontTools version from '<=' to '==' to accept more versions

Author: kaydeearts

requirements.txt

@@ -6,7 +6,7 @@ lxml==4.9.2
 booleanOperations==0.9.0
 defcon[lxml,pens]==0.10.2
 fontMath==0.9.3
-fontTools[unicode,woff,lxml,ufo]<=4.39.4
+fontTools[unicode,woff,lxml,ufo]==4.39.4
 psautohint==2.4.0
 tqdm==4.65.0
 ufonormalizer==0.6.1