环境变量调整为 LEANCLOUD_ 前缀

[juvenn]

• 环境变量调整 LC -> LEANCLOUD
• 从 LEANCLOUD_API_SERVER 获取 api endpoint
• 根据环境变量设置 x-lc-prod
• 异常单独打印错误消息

[codecov-io]

Codecov Report

Merging #151 into master will decrease coverage by 1.34%. The diff coverage is 20%.

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
- Coverage   67.69%   66.35%   -1.35%     
==========================================
  Files          33       33              
  Lines        2133     2428     +295     
==========================================
+ Hits         1444     1611     +167     
- Misses        689      817     +128

Impacted Files	Coverage Δ
src/LeanCloud/Engine/LeanEngine.php	0% <0%> (ø)	:arrow_up:
src/LeanCloud/Client.php	82.35% <33.33%> (-2.8%)	:arrow_down:
src/LeanCloud/Storage/SessionStorage.php	55.55% <0%> (-5.99%)	:arrow_down:
src/LeanCloud/User.php	77.9% <0%> (-1.73%)	:arrow_down:
src/LeanCloud/BatchRequestError.php	63.63% <0%> (-1.37%)	:arrow_down:
src/LeanCloud/Object.php	90.17% <0%> (-1.16%)	:arrow_down:
src/LeanCloud/Relation.php	69.56% <0%> (-0.44%)	:arrow_down:
src/LeanCloud/Operation/ArrayOperation.php	89.65% <0%> (-0.22%)	:arrow_down:
... and 22 more

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[juvenn]

Approve

[juvenn]

Approved