Update backports.functools-lru-cache from 1.2.1 to 1.5

Author: pyup-bot

requirements.txt

@@ -4,7 +4,7 @@ arrow==0.12.0
 asn1crypto==0.24.0
 attrs==17.4.0
 Babel==2.5.2
-backports.functools-lru-cache==1.2.1
+backports.functools-lru-cache==1.5
 binaryornot==0.4.4
 bumpversion==0.5.3
 certifi==2017.11.5