fix(flex-offset): correct type when using with 'strictNullChecks' (#929)

Author: Teamop

src/apps/demo-app/tsconfig.json

@@ -7,6 +7,7 @@
     "moduleResolution": "node",
     "emitDecoratorMetadata": true,
     "experimentalDecorators": true,
+    "strictNullChecks": true,
     "target": "es5",
     "typeRoots": [
       "node_modules/@types"
@@ -18,4 +19,4 @@
     "module": "es2015",
     "baseUrl": "./"
   }
-}
+}

src/lib/flex/flex-offset/flex-offset.ts

@@ -41,8 +41,8 @@ export class FlexOffsetStyleBuilder extends StyleBuilder {
       offset = offset + '%';
     }
     const horizontalLayoutKey = parent.isRtl ? 'margin-right' : 'margin-left';
-    const styles = isFlowHorizontal(parent.layout) ? {[horizontalLayoutKey]: `${offset}`} :
-      {'margin-top': `${offset}`};
+    const styles: StyleDefinition = isFlowHorizontal(parent.layout) ?
+      {[horizontalLayoutKey]: `${offset}`} : {'margin-top': `${offset}`};
 
     return styles;
   }