Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/.solcover.js

@@ -0,0 +1,13 @@
+module.exports = {
+  norpc: true,
+  testCommand: 'npm test',
+  compileCommand: 'npm run compile',
+  skipFiles: ['mocks'],
+  providerOptions: {
+    default_balance_ether: '10000000000000000000000000',
+  },
+  mocha: {
+    fgrep: '[skip-on-coverage]',
+    invert: true,
+  },
+};