btcmarkets: remove trailing slash on markets/ticker strings and update endpoint pathways

[shazbert]

PR Description

BTC markets woke up one day and banned the trailing slash. This hopefully appeases the BTCM gods.

Fixes # (issue)

Type of change

Please delete options that are not relevant and add an x in [] as item is complete.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration and
also consider improving test coverage whilst working on a certain feature or package.

• go test ./... -race
• golangci-lint run
• Test X

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation and regenerated documentation via the documentation tool
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally and on Github Actions with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.02%. Comparing base (1e95ae9) to head (3ea45ef).
Report is 1 commits behind head on master.

❗ Current head 3ea45ef differs from pull request most recent head a53bea7. Consider uploading reports for the commit a53bea7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1530      +/-   ##
==========================================
- Coverage   37.91%   36.02%   -1.90%     
==========================================
  Files         411      411              
  Lines      147198   176914   +29716     
==========================================
+ Hits        55817    63740    +7923     
- Misses      83588   105395   +21807     
+ Partials     7793     7779      -14     

Files	Coverage Δ
exchanges/btcmarkets/btcmarkets.go	24.14% <100.00%> (-1.08%)	⬇️

... and 387 files with indirect coverage changes

[gloriousCode]

shazbert.com/tACK!/

[thrasher-]

tACK all changed endpoints! Just a minor suggestion