Require PHP 7 to support whitelists/blacklists

From the PHP manual:

```
In PHP 5, value must be a scalar value.... In PHP 7, array values are also accepted.
```

.travis.yml

@@ -14,17 +14,13 @@ cache:
 
 matrix:
   include:
+    - php: nightly
+      env: WP_VERSION=latest
     - php: 7.1
       env: WP_VERSION=latest
     - php: 7.0
       env: WP_VERSION=latest
-    - php: 5.6
-      env: WP_VERSION=4.4
-    - php: 5.6
-      env: WP_VERSION=latest
-    - php: 5.6
-      env: WP_VERSION=trunk
-    - php: 5.6
+    - php: 7.1
       env: WP_TRAVISCI=phpcs
 
 before_script:

README.md

@@ -3,7 +3,7 @@
 **Tags:** wp-cli, cli, cron, cron control  
 **Requires at least:** 4.8.1  
 **Tested up to:** 4.9  
-**Requires PHP:** 5.6  
+**Requires PHP:** 7.0  
 **Stable tag:** 0.1.0  
 **License:** GPLv2 or later  
 **License URI:** http://www.gnu.org/licenses/gpl-2.0.html  
@@ -23,6 +23,10 @@ Provides a WP-CLI command to schedule these events. A UI is under consideration.
 
 ## Frequently Asked Questions ##
 
+### Why is PHP 7 required? ###
+
+To support arrays in constants set using `define()`, PHP 7 is required. These are used to set whitelists and blacklists, though filters are also provided; see below.
+
 ### Does this support custom WP-CLI commands? ###
 
 Yes. By default, no restrictions are placed on what commands are supported, as those restrictions depend on the environment where this plugin is used. That said, see the following sections regarding support for whitelists and blacklists.

readme.txt

@@ -3,7 +3,7 @@ Contributors: ethitter, automattic
 Tags: wp-cli, cli, cron, cron control
 Requires at least: 4.8.1
 Tested up to: 4.9
-Requires PHP: 5.6
+Requires PHP: 7.0
 Stable tag: 0.1.0
 License: GPLv2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html
@@ -23,6 +23,10 @@ Provides a WP-CLI command to schedule these events. A UI is under consideration.
 
 == Frequently Asked Questions ==
 
+= Why is PHP 7 required? =
+
+To support arrays in constants set using `define()`, PHP 7 is required. These are used to set whitelists and blacklists, though filters are also provided; see below.
+
 = Does this support custom WP-CLI commands? =
 
 Yes. By default, no restrictions are placed on what commands are supported, as those restrictions depend on the environment where this plugin is used. That said, see the following sections regarding support for whitelists and blacklists.