add goconst. maybe some improvements needed

.golangci.yml

@@ -17,8 +17,17 @@ linters:
   enable:    
     - errcheck
     - govet
+    - goconst
 
 linters-settings:
+  goconst: 
+    min-len: 2
+    min-occurrences: 2
+    ignore-tests: true
+    numbers: true
+    min: 2
+    max: 1000000
+    ignore-calls: false
   errcheck:
     exclude-functions:
     - (io.Closer).Close