Prepare for editor.save becoming async (#64)

* Prepare for `editor.save` becoming async

Fixes #63

This fix should be both backcompatible and forwardcompatible, as returning something that's not a promise from a promise callback will resolve immediately, whereas returning a promise will wait for the promise, so it should do the right thing whether save is sync or async.

* Install libstdc++6 for electron

* Disable testing beta atom

* Need to return the promise from `getCompletions` -.-

.travis.yml

@@ -8,11 +8,8 @@ cache:
     - node_modules
 
 script:
+  - sudo apt-get install libstdc++6
   - npm run build && rm -r node_modules
   - curl -s -O https://raw.githubusercontent.com/atom/ci/master/build-package.sh
   - chmod u+x build-package.sh
   - ./build-package.sh
-
-env:
-  matrix:
-    - ATOM_CHANNEL=beta

spec/auto-completer-spec.js

@@ -31,15 +31,18 @@ describe('Autocompleter', () => {
   const LAST_LINE_IN_TEMPLATE = 12;
 
   const getCompletions = () => {
-    editor.save();
-    const cursor = editor.getLastCursor();
-    const start = cursor.getBeginningOfCurrentWordBufferPosition();
-    const end = cursor.getBufferPosition();
-    return provider.getSuggestions({
-      editor: editor,
-      bufferPosition: end,
-      scopeDescriptor: cursor.getScopeDescriptor(),
-      prefix: editor.getTextInRange([start, end])
+    return Promise.resolve().then(() => {
+      return editor.save();
+    }).then(() => {
+      const cursor = editor.getLastCursor();
+      const start = cursor.getBeginningOfCurrentWordBufferPosition();
+      const end = cursor.getBufferPosition();
+      return provider.getSuggestions({
+        editor: editor,
+        bufferPosition: end,
+        scopeDescriptor: cursor.getScopeDescriptor(),
+        prefix: editor.getTextInRange([start, end])
+      });
     }).catch(e => {
       console.error(e);
       throw e;