use GetBackingStore() instead of GetContents() (#888)

* use GetBackingStore() instead of GetContents()

Use GetBackingStore() instead of GetContents() for v8 >= 8.0
as GetContents() has been deprecated. Node.js 14 will use 8.1

It would be possible to use GetBackingStore() already with 7.9
but this would lead to issues with Node.js 13 as it uses 7.8
till 13.2.0.

Additionally update testmatrix to use latest electron versions
and add electron 8.

Co-authored-by: Ben Noordhuis <info@bnoordhuis.nl>

.travis.yml

@@ -26,9 +26,10 @@ env:
   - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="2.0.18"
   - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="3.1.13"
   - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="4.2.12"
-  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="5.0.11"
-  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="6.1.2"
-  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="7.0.0"
+  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="5.0.13"
+  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="6.1.9"
+  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="7.1.14"
+  - TRAVIS_NODE_VERSION="lts/*" ELECTRON_VERSION="8.0.3"
 matrix:
   exclude:
     - os: osx

nan_typedarray_contents.h

@@ -31,7 +31,13 @@ class TypedArrayContents {
       v8::Local<v8::ArrayBuffer> buffer = array->Buffer();
 
       length = byte_length / sizeof(T);
-      data   = static_cast<char*>(buffer->GetContents().Data()) + byte_offset;
+// Actually it's 7.9 here but this would lead to ABI issues with Node.js 13
+// using 7.8 till 13.2.0.
+#if (V8_MAJOR_VERSION >= 8)
+      data = static_cast<char*>(buffer->GetBackingStore()->Data()) + byte_offset;
+#else
+      data = static_cast<char*>(buffer->GetContents().Data()) + byte_offset;
+#endif
     }
 
 #else