travis: explicitly test against 7.4

[m6w6/ext-propro] / travis / pecl

diff --git a/travis/pecl b/travis/pecl
index 309d295271f95d9267c64535de8c2e638f6614cc..54a746ab5e068060f53796d0aca55f76656bb8b1 160000 (submodule)
--- a/travis/pecl
+++ b/travis/pecl
@@ -1 +1 @@
-Subproject commit 309d295271f95d9267c64535de8c2e638f6614cc
+Subproject commit 54a746ab5e068060f53796d0aca55f76656bb8b1