fix(deps): bump google-gax to 1.7.5 (#558)

Author: JustinBeckwith

package.json

@@ -56,7 +56,7 @@
     "dot-prop": "^5.0.0",
     "escape-string-regexp": "^2.0.0",
     "extend": "^3.0.2",
-    "google-gax": "^1.6.3",
+    "google-gax": "^1.7.5",
     "is": "^3.0.1",
     "is-utf8": "^0.2.1",
     "lodash.snakecase": "^4.1.1",