travis+lint+make: limit lint concurrency only on travis

Since linting is much faster by using the defaults locally.

.golangci.yml

@@ -2,10 +2,6 @@ run:
   # timeout for analysis
   deadline: 4m
 
-  # Linting uses a lot of memory. Keep it under control by only running a single
-  # worker.
-  concurrency: 1
-
   # Skip autogenerated files for mobile.
   skip-files:
     - "mobile\\/.*generated\\.go"

.travis.yml

@@ -41,7 +41,7 @@ jobs:
       script:
         - make rpc-check
         - make unit pkg=... case=_NONE_
-        - make lint
+        - make lint workers=1
         - make btcd
         - LNDBUILDSYS=windows-amd64 bash ./build/release/release.sh
     - stage: Test

Makefile

@@ -51,7 +51,13 @@ include make/testing_flags.mk
 
 DEV_TAGS := $(if ${tags},$(DEV_TAGS) ${tags},$(DEV_TAGS))
 
-LINT = $(LINT_BIN) run -v
+# Linting uses a lot of memory, so keep it under control by limiting the number
+# of workers if requested.
+ifneq ($(workers),)
+LINT_WORKERS = --concurrency=$(workers)
+endif
+
+LINT = $(LINT_BIN) run -v $(LINT_WORKERS)
 
 GREEN := "\\033[0;32m"
 NC := "\\033[0m"