Fallback to Microsoft Edge for Linux

[yhatt]

Continue from #199. Microsoft Edge for Linux is available now.
https://blogs.windows.com/msedgedev/2020/10/20/microsoft-edge-dev-linux/

Currently Marp CLI is supporting fallback to Edge only in Windows, macOS, and Linux on WSL1 (use host Windows Edge). We have to find out Linux Edge binary when executing Marp CLI on Linux.

marp-cli/src/utils/edge-finder.ts

Line 27 in 9bb91e6

// TODO: Find out Microsoft Edge for Linux

According to Microsoft's Edge dev tools for VS Code, Linux binary seems to be located in /opt/Microsoft/msedge(-channel)/msedge (in the case of Debian).
https://github.com/microsoft/vscode-edge-devtools/blob/f586583f90bf5307c0e625dc0c94a974a0b2d862/src/utils.ts#L529-L560