[#96] .golangci.yml: Fix deprecated config options

```
WARN [config_reader] The configuration option `run.skip-files` is deprecated, please use `issues.exclude-files`.
WARN [config_reader] The configuration option `output.format` is deprecated, please use `output.formats`
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

.golangci.yml

@@ -9,13 +9,11 @@ run:
   # include test files or not, default is true
   tests: false
 
-  skip-files:
-    - (^|.*/)grpc/(.*)
-
 # output configuration options
 output:
   # colored-line-number|line-number|json|tab|checkstyle|code-climate, default is "colored-line-number"
-  format: tab
+  formats:
+    - format: tab
 
 # all available settings of specific linters
 linters-settings:
@@ -67,6 +65,9 @@ linters:
   fast: false
 
 issues:
+  exclude-files:
+    - (^|.*/)grpc/(.*)
+
   # Excluding configuration per-path, per-linter, per-text and per-source
   exclude-rules:
     - path: v2 # ignore stutters in universal structures due to protobuf compatibility