Fix examples of push gateway in README.md

[mrfussion]

It's a simple correction in the examples so that newbies don't get frustrated :)

i change .then({ resp, body } => { for .then(({ resp, body }) => { in all examples

specific error:

.then({ resp, body } => {
            ^^^^^^^^^^^^^

SyntaxError: Malformed arrow function parameter list
    at wrapSafe (internal/modules/cjs/loader.js:915:16)
    at Module._compile (internal/modules/cjs/loader.js:963:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)
    at Module.load (internal/modules/cjs/loader.js:863:32)
    at Function.Module._load (internal/modules/cjs/loader.js:708:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12)
    at internal/main/run_main_module.js:17:47

[zbjornson]

Thanks!