fix mocha 8.0.0 does not support Node version < 6

scripts/build-appveyor.bat

@@ -106,7 +106,8 @@ GOTO NPM_TEST_FINISHED
 ECHO installing electron
 CALL npm install -g "electron@%NODE_RUNTIME_VERSION%"
 ECHO installing electron-mocha
-CALL npm install -g electron-mocha
+IF "%nodejs_version%" LEQ 6 CALL npm install -g "electron-mocha@7"
+IF "%nodejs_version%" GTR 6 CALL npm install -g "electron-mocha"
 ECHO preparing tests
 CALL electron "test/support/createdb-electron.js"
 DEL "test\support\createdb-electron.js"

scripts/build_against_electron.sh

@@ -18,7 +18,11 @@ function publish() {
 
 function electron_pretest() {
     npm install -g electron@${ELECTRON_VERSION}
+    if [ "$NODE_VERSION" -le 6 ]; then
+        npm install -g electron-mocha@7
+    else
         npm install -g electron-mocha
+    fi
     if [ "${TRAVIS_OS_NAME}" = "osx" ]; then 
         (sudo Xvfb :99 -ac -screen 0 1024x768x8; echo ok )&
     else