shebang should be specific to python version (PEP394)

preferred form is #!/usr/bin/env python3 as gnucash now only works with
python3

bindings/python/example_scripts/gnc_convenience.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 # -*- coding: UTF-8 -*-
 
 ##@file

bindings/python/example_scripts/latex_invoices.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 ##@file

bindings/python/example_scripts/new_book_with_opening_balances.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # new_book_with_opening_balances.py -- Replicate the account structure of a
 # book and apply basis opening balances from the original

bindings/python/example_scripts/priceDB_test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Test file for price database stuff
 # To update the price database call
 # $PATH/gnucash  --add-price-quotes $PATHTOFILE

bindings/python/example_scripts/price_database_example.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Another test file for price database stuff
 # To update the price database call
 # $PATH/gnucash  --add-price-quotes $PATHTOFILE

bindings/python/example_scripts/quotes_historic.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # quotes_historic.py -- Example Script to read historic quote data into gnucash
 #

bindings/python/example_scripts/rest-api/gnucash_rest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
 '''
 

bindings/python/example_scripts/simple_book.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 ##  @file
 #   @brief Simple example for a book 

bindings/python/example_scripts/simple_business_create.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # simple_business_create.py -- Set up a set of books for business feature use
 #

bindings/python/example_scripts/simple_invoice_insert.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # simple_invoice_insert.py -- Add an invoice to a set of books
 #

bindings/python/example_scripts/simple_session.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 ##  @file
 #   @brief Example Script simple session
 #   @ingroup python_bindings_examples

bindings/python/example_scripts/simple_sqlite_create.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 ##  @file
 #   @brief Example Script simple sqlite create 
 #   @ingroup python_bindings_examples

bindings/python/example_scripts/simple_test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 ## @file
 # @brief Creates a basic set of accounts and a couple of transactions
 # @ingroup python_bindings_examples