Google needs 50 years on certificates - let's give them a bit more th…

…an that

cmd/fyne/internal/mobile/cert.go

@@ -29,6 +29,7 @@ func signPKCS7(rand io.Reader, priv *rsa.PrivateKey, msg []byte) ([]byte, error)
 		SerialNumber:       big.NewInt(serialNumber),
 		SignatureAlgorithm: x509.SHA1WithRSA,
 		Subject:            name,
+		NotAfter:           time.Date(2120, time.January, 1, 12, 0, 0, 0, time.UTC), // more than 50 years for Google Play Store
 	}
 
 	b, err := x509.CreateCertificate(rand, template, template, priv.Public(), priv)