Update bug report template for github

Summary: It mention bitcoin core, which is obviously outdated.

Test Plan: \o/

Reviewers: schancel, Mengerian, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Subscribers: freetrader

Differential Revision: https://reviews.bitcoinabc.org/D696

.github/ISSUE_TEMPLATE.md

@@ -1,10 +1,10 @@
 <!--- Remove sections that do not apply -->
 
-This issue tracker is only for technical issues related to bitcoin-core.
+This issue tracker is only for technical issues related to bitcoin-abc.
 
 General bitcoin questions and/or support requests and are best directed to the [Bitcoin StackExchange](https://bitcoin.stackexchange.com).
 
-For reporting security issues, please read instructions at [https://bitcoincore.org/en/contact/](https://bitcoincore.org/en/contact/).
+For reporting security issues, please contact people privately.
 
 ### Describe the issue
 
@@ -23,7 +23,7 @@ Tell us what happens instead
 ### Screenshots.
 If the issue is related to the GUI, screenshots can be added to this issue via drag & drop.
 
-### What version of bitcoin-core are you using?
+### What version of bitcoin-abc are you using?
 List the version number/commit ID, and if it is an official binary, self compiled or a distribution package such as PPA.
 
 ### Machine specs: