license: Use LGPL-2.1+ instead of LGPL-3.0+

This matches the GTK+ and GLib licenses, helping us to contribute code
to these libraries if needed and simplifying license management.

src/handy.h

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HANDY_H

src/hdy-dialer-button.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <glib/gi18n.h>

src/hdy-dialer-button.h

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HDY_DIALER_BUTTON_H

src/hdy-dialer-cycle-button.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <glib/gi18n.h>

src/hdy-dialer-cycle-button.h

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HDY_DIALER_CYCLE_BUTTON_H

src/hdy-dialer.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <glib/gi18n.h>

src/hdy-dialer.h

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HDY_DIALER_H

src/hdy-string-utf8.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <stdlib.h>

src/hdy-string-utf8.h

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HDY_STRING_UTF8_H

src/hdy-version.h.in

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #ifndef HDY_VERSION_H

tests/test-dialer-cycle-button.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <handy.h>

tests/test-dialer.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <handy.h>

tests/test-string-utf8.c

 /*
  * Copyright (C) 2017 Purism SPC
  *
- * SPDX-License-Identifier: LGPL-3.0+
+ * SPDX-License-Identifier: LGPL-2.1+
  */
 
 #include <handy.h>