replace travis with Github Actions (#1432)

replace travis with Github Actions

scripts/diffcheck.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+diff README.mediawiki /tmp/table.mediawiki | grep '^[<>] |' >/tmp/after.diff || true
+if git checkout HEAD^ && scripts/buildtable.pl >/tmp/table.mediawiki 2>/dev/null; then
+    diff README.mediawiki /tmp/table.mediawiki | grep '^[<>] |' >/tmp/before.diff || true
+    newdiff=$(diff -s /tmp/before.diff /tmp/after.diff -u | grep '^+')
+    if [ -n "$newdiff" ]; then
+        echo "$newdiff"
+        exit 1
+    fi
+else
+    echo 'Cannot build previous commit table for comparison'
+fi