Make travis/jenkins check for lint on files which are clean to start with

scripts/generate-eslint-error-ignore-file

@@ -0,0 +1,21 @@
+#!/bin/sh
+#
+# generates .eslintignore.errorfiles to list the files which have errors in,
+# so that they can be ignored in future automated linting.
+
+out=.eslintignore.errorfiles
+
+cd `dirname $0`/..
+
+echo "generating $out"
+
+{
+    cat <<EOF
+# autogenerated file: run scripts/generate-eslint-error-ignore-file to update.
+
+EOF
+    
+    ./node_modules/.bin/eslint --no-ignore -f json src test |
+        jq -r '.[] | select((.errorCount + .warningCount) > 0) | .filePath' |
+        sed -e 's/.*matrix-react-sdk\///';
+} > "$out"