Retire older Go versions.

.travis.yml

@@ -1,32 +1,32 @@
 language: go
 sudo: false
 go:
-- '1.10'
-- '1.11'
-- '1.12'
-- '1.13'
-- master
+  - "1.12"
+  - "1.13"
+  - "1.14"
+  - "1.15"
+  - master
 
 install:
-- go get github.com/pkg/errors
-# golint is no longer available for go versions 1.7 and 1.8
-- |
-  INSTALLED_GO_VERSION=`go version | sed 's/go version go\(.*\) .*/\1/'`
-  echo $INSTALLED_GO_VERSION
-  if [ "$INSTALLED_GO_VERSION" != "1.7" ] && [ "$INSTALLED_GO_VERSION" != "1.8" ]; then
-    go get golang.org/x/lint/golint
-  fi
+  - go get github.com/pkg/errors
+  # golint is no longer available for go versions 1.7 and 1.8
+  - |
+    INSTALLED_GO_VERSION=`go version | sed 's/go version go\(.*\) .*/\1/'`
+    echo $INSTALLED_GO_VERSION
+    if [ "$INSTALLED_GO_VERSION" != "1.7" ] && [ "$INSTALLED_GO_VERSION" != "1.8" ]; then
+      go get golang.org/x/lint/golint
+    fi
 
 before_script:
-- |
-  which golint;
-  if [ $? == 0 ]; then
-    golint ./...
-  fi
-  go vet
+  - |
+    which golint;
+    if [ $? == 0 ]; then
+      golint ./...
+    fi
+    go vet
 
 script:
-- go test -v -race -coverprofile=coverage.txt -covermode=atomic
+  - go test -v -race -coverprofile=coverage.txt -covermode=atomic
 
 after_success:
-- bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)