Change wifi example to build only DISCO_L475VG_IOT01A

Author: Jussi Siponen

tools/test/examples/examples.json

@@ -116,7 +116,7 @@
       "sub-repo-example": false,
       "subs": [],
       "features" : [],
-      "targets" : [],
+      "targets" : ["DISCO_L475VG_IOT01A"],
       "toolchains" : [],
       "exporters": [],
       "compile" : true,