test: fix version constraints

mle86 · mle86 · commit f6cd3be69e1d · 2019-10-23T20:42:17.000+02:00
While the code itself works fine with PHP 7.0,
PHPUnit 7 does not.
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,6 @@
 language: php
 
 php:
-  - '7.0'
   - '7.1'
   - '7.2'
   - '7.3'

-Original file line number
+Diff line change
@@ @@ -1,7 +1,6 @@ @@
 language: php
 php:
 -  - '7.0'
   - '7.1'
   - '7.2'
   - '7.3'