fix(build): Use POSIX compatible comparison

In CI were errors/warnings like:

    ./scripts/plugins.sh: 7: [: windowsx: unexpected operator

This comparison is compatible with more versions of bash and other
shells and should prevent these messages.

scripts/plugins.sh

@@ -4,7 +4,7 @@
 set -e
 
 BINARY_SUFFIX=""
-if [ "${GOOS}x" == "windowsx" ]; then
+if [ "${GOOS}x" = "windowsx" ]; then
     BINARY_SUFFIX=".exe"
 fi