Refresh pacman in the appveyor build (#84)

...for updated Go package versions. Go 1.12 is gone from the MSYS2 repos.

.appveyor/install.sh

@@ -6,9 +6,11 @@ export GOROOT=/mingw64/lib/go
 export GOPATH=/go
 export CGO_ENABLED=1
 
+set -x
+
 pacman --noconfirm -S \
-    mingw64/mingw-w64-x86_64-go \
-    mingw64/mingw-w64-x86_64-libusb
+    mingw-w64-x86_64-go \
+    mingw-w64-x86_64-libusb
 
 go version
 go get -t github.com/google/gousb/...

.appveyor/upgrade_pacman.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+export PATH="/mingw64/bin:${PATH}"
+set -x
+curl -O https://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz
+curl -O https://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig
+pacman-key --verify msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz.sig &&\
+pacman --noconfirm -U msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz
+pacman --noconfirm -Syy pacman

appveyor.yml

@@ -3,6 +3,7 @@ platform: x64
 clone_folder: C:\msys64\go\src\github.com\google\gousb
 
 install:
-  - C:\msys64\usr\bin\bash.exe -lc "cd /go/src/github.com/google/gousb/ && .appveyor/./install.sh"
+  - C:\msys64\usr\bin\bash.exe -l /go/src/github.com/google/gousb/.appveyor/upgrade_pacman.sh
+  - C:\msys64\usr\bin\bash.exe -lc "cd /go/src/github.com/google/gousb/ && .appveyor/install.sh"
 
 build: off