scripts: use python3 in shebang

As most of oe-test cases work for devtool and recipetool
it makes sense to switch both tools to python 3 by
explicitly referring to python3 in their shebangs.

(From OE-Core rev: dad9617809c60ec5f11d4780b0afa1cffa1efed5)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/buildhistory-diff

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Report significant differences in the buildhistory repository since a specific revision
 #

scripts/devtool

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # OpenEmbedded Development tool
 #

scripts/oe-pkgdata-util

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # OpenEmbedded pkgdata utility
 #

scripts/recipetool

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Recipe creation tool
 #