Drop support for PHP 7.0

.travis.yml

@@ -5,7 +5,6 @@ group: edge
 language: php
 
 php:
-  - 7.0
   - 7.1
   - 7.2
   - nightly

README.md

@@ -9,6 +9,10 @@ This PHP extension provides a set of useful functional-style operations on PHP a
 
 Method names and functionalities are inspired by [Kotlin.Collections](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/).
 
+### 1.1 Notes
+
+* This extension requires PHP 7.1 and above.
+
 ## 2. Documentation
 
 ### 2.1 Functionalities