appveyor: bump to Go 1.12.6 (#19709)

* appveyor: bump to Go 1.12.6

* vendor/vendor.json: govendor fetch github.com/karalabe/usb/^

appveyor.yml

@@ -23,8 +23,8 @@ environment:
 install:
   - git submodule update --init
   - rmdir C:\go /s /q
-  - appveyor DownloadFile https://dl.google.com/go/go1.12.5.windows-%GETH_ARCH%.zip
-  - 7z x go1.12.5.windows-%GETH_ARCH%.zip -y -oC:\ > NUL
+  - appveyor DownloadFile https://dl.google.com/go/go1.12.6.windows-%GETH_ARCH%.zip
+  - 7z x go1.12.6.windows-%GETH_ARCH%.zip -y -oC:\ > NUL
   - go version
   - gcc --version
 

vendor/github.com/karalabe/usb/appveyor.yml

@@ -22,8 +22,8 @@ environment:
 
 install:
   - rmdir C:\go /s /q
-  - appveyor DownloadFile https://storage.googleapis.com/golang/go1.12.5.windows-%GOARCH%.zip
-  - 7z x go1.12.5.windows-%GOARCH%.zip -y -oC:\ > NUL
+  - appveyor DownloadFile https://storage.googleapis.com/golang/go1.12.6.windows-%GOARCH%.zip
+  - 7z x go1.12.6.windows-%GOARCH%.zip -y -oC:\ > NUL
   - go version
   - gcc --version
 

vendor/vendor.json

@@ -243,10 +243,10 @@
 			"revisionTime": "2017-04-30T22:20:11Z"
 		},
 		{
-			"checksumSHA1": "wqKuSmlxa4hVZwfs4ZjtKtM5Yp0=",
+			"checksumSHA1": "TU/WaqL7fYPDovmGVRSo8btD4ZM=",
 			"path": "github.com/karalabe/usb",
-			"revision": "3eff4807c21acef1c5f1b712a225ab09a8961504",
-			"revisionTime": "2019-06-07T09:24:32Z",
+			"revision": "4d6ba34a841453237dba721eeec1af0ef9a7a890",
+			"revisionTime": "2019-06-13T07:02:55Z",
 			"tree": true
 		},
 		{