Update minimum support php version to 5.5

php/ext/google/protobuf/package.xml

@@ -45,7 +45,7 @@ First alpha release.
  <dependencies>
   <required>
    <php>
-    <min>5.6.0</min>
+    <min>5.5.37</min>
    </php>
    <pearinstaller>
     <min>1.4.0</min>