Enable the unconvert, misspell, and nakedret linters

They seem fairly reasonable in what they do.

Signed-off-by: Nic Cope <negz@rk0n.org>

.golangci.yml

@@ -111,12 +111,9 @@ linters:
     - gofmt  # We enable this as well as goimports for its simplify mode.
     - prealloc
     - golint
-  enable-all: false
-
-  disable:
-    - maligned
-    # - prealloc
-  disable-all: false
+    - unconvert
+    - misspell
+    - nakedret
 
   presets:
     - bugs