Upgrade curl to test HTTP2 about httpstat

[reorx]

Achieve the ability to indicate curl bin path in PR #13.

Set curl bin by:

export HTTPSTAT_CURL_BIN=/usr/local/Cellar/curl/7.50.3/bin/curl

Request https://http2.akamai.com/ with curl option --http2

$ python httpstat.py https://http2.akamai.com/ --http2
DEBUG:httpstat:ENVs:
  HTTPSTAT_SHOW_BODY: False
  HTTPSTAT_SHOW_SPEED: False
  HTTPSTAT_CURL_BIN: /usr/local/Cellar/curl/7.50.3/bin/curl
  HTTPSTAT_DEBUG: True

DEBUG:httpstat:cmd: ['/usr/local/Cellar/curl/7.50.3/bin/curl', '-w', '{\n"time_namelookup": %{time_namelookup},\n"time_connect": %{time_connect},\n"time_appconnect": %{time_appconnect},\n"time_pretransfer": %{time_pretransfer},\n"time_redirect": %{time_redirect},\n"time_starttransfer": %{time_starttransfer},\n"time_total": %{time_total},\n"speed_download": %{speed_download},\n"speed_upload": %{speed_upload}\n}', '-D', '/var/folders/82/sfpvl4pd3vd4_4hy0dqcvldr0000gn/T/tmpZBoEIw', '-o', '/var/folders/82/sfpvl4pd3vd4_4hy0dqcvldr0000gn/T/tmpLgR7O9', '-s', '-S', '--http2', 'https://http2.akamai.com/']

HTTP/2 200
server: Apache
content-type: text/html;charset=UTF-8
etag: "5e9139516a4f3d7a27577441623ca90d:1465962509"
link: <https://ds-aksb-a.akamaihd.net>;rel="preconnect"
link: <https://www.youtube.com>;rel="preconnect"
strict-transport-security: max-age=31536000 ; includeSubDomains
access-control-allow-origin: *
access-control-allow-methods: GET,HEAD,POST
access-control-allow-headers: *
access-control-allow-credentials: false
access-control-max-age: 86400
accept-ch: DPR, Width, Viewport-Width, Downlink, Save-Data
protocol_negotiation: h2
myproto: h2
client_ip: 119.9.108.90
client_real_ip: 119.9.108.90
ghost_service_ip: 184.28.218.196
ghost_ip: 23.196.42.197
rtt: 4
push: true
x-akamai-transformed: 9 10583 0 pmb=mRUM,1
cache-control: max-age=43200
expires: Tue, 27 Sep 2016 19:23:27 GMT
date: Tue, 27 Sep 2016 07:23:27 GMT
content-length: 11692

Body stored in: /var/folders/82/sfpvl4pd3vd4_4hy0dqcvldr0000gn/T/tmpLgR7O9

  DNS Lookup   TCP Connection   SSL Handshake   Server Processing   Content Transfer
[    478ms   |       4ms      |     77ms      |       635ms       |        0ms       ]
             |                |               |                   |                  |
    namelookup:478ms          |               |                   |                  |
                        connect:482ms         |                   |                  |
                                    pretransfer:559ms             |                  |
                                                      starttransfer:1194ms           |
                                                                                 total:1194ms