Update core "requires" and "tested up to" versions

We don't really *require* 4.5, per se, but we know that the plugin will
throw some deprecated notices in WP <4.5, so CI'm specifying 4.5 as the
minimum version supported.

README.md

@@ -1,8 +1,8 @@
 # Shortcake (Shortcode UI) #
 **Contributors:** fusionengineering, mattheu, danielbachhuber, zebulonj, goldenapples, jitendraharpalani, sanchothefat, bfintal, davisshaver, garyj, mte90, fredserva, khromov  
 **Tags:** shortcodes  
-**Requires at least:** 4.3  
-**Tested up to:** 4.4  
+**Requires at least:** 4.5  
+**Tested up to:** 4.7  
 **Stable tag:** 0.7.0  
 **License:** GPLv2 or later  
 **License URI:** http://www.gnu.org/licenses/gpl-2.0.html  

readme.txt

@@ -1,8 +1,8 @@
 === Shortcake (Shortcode UI) ===
 Contributors: fusionengineering, mattheu, danielbachhuber, zebulonj, goldenapples, jitendraharpalani, sanchothefat, bfintal, davisshaver, garyj, mte90, fredserva, khromov
 Tags: shortcodes
-Requires at least: 4.3
-Tested up to: 4.4
+Requires at least: 4.5
+Tested up to: 4.7
 Stable tag: 0.7.0
 License: GPLv2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html