line: use data domain to get media and menu content

[chentsulin]

To avoid the domain name breaking changes introduced by LINE, port those changes into v0.7.x for Bottender v0.15.x.

#550
Change the endpoint of api call in the following methods:

• LineClient#getMessageContent
• LineClient#uploadRichMenuImage
• LineClient#downloadRichMenuImage

[codecov]

Codecov Report

Merging #557 into v0.7.x will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           v0.7.x     #557      +/-   ##
==========================================
+ Coverage   97.52%   97.54%   +0.01%     
==========================================
  Files          13       13              
  Lines         930      936       +6     
  Branches      124      124              
==========================================
+ Hits          907      913       +6     
  Misses         22       22              
  Partials        1        1              

Impacted Files	Coverage Δ
packages/messaging-api-line/src/LineClient.js	99.24% <100.00%> (+0.03%)	⬆️

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