Tweak golangci-lint: exclude Log statements from errcheck

.errcheck-exclude.txt

@@ -0,0 +1,3 @@
+// the following functions will be excluded from errcheck
+// https://github.com/kisielk/errcheck#excluding-functions
+(github.com/go-kit/kit/log.Logger).Log

.golangci.yml

@@ -61,6 +61,10 @@ linters:
     - interfacer
     - typecheck
 
+linters-settings:
+  errcheck:
+    exclude: ./.errcheck-exclude.txt
+
 issues:
   exclude:
     - Error return value of .*log\.Logger\)\.Log\x60 is not checked