Update boto3 requirement from ~=1.15.15 to ~=1.15.18 (#600)

dependabot[bot] · web-flow · commit 2e8fa093c333 · 2020-10-17T12:09:06.000+02:00
diff --git a/requirements/requirements.txt b/requirements/requirements.txt
@@ -1,4 +1,4 @@
-boto3~=1.15.15
+boto3~=1.15.18
 cryptography==3.1.1
 marshmallow==3.8.0
 packaging==20.4
