Can't install on systems where python = python3

[brandoncurtis]

Installation fails on machines where python=python3 because of node-gyp's lack of support for python3 nodejs/node-gyp#1687

~/repos/esplora$ npm install                                                                                                                                                                                                                                     
                                                                                                                                 
> esplora@0.1.0 postinstall /home/brandon/repos/esplora
> (cd client && npm install) && (cd prerender-server && npm install)
           
                        
> canvas@1.6.13 install /home/brandon/repos/esplora/client/node_modules/canvas                                    
> node-gyp rebuild                                
                              
gyp ERR! configure error
gyp ERR! stack Error: Command failed: /usr/bin/python -c import sys; print "%s.%s.%s" % sys.version_info[:3];
gyp ERR! stack   File "<string>", line 1                                                          
gyp ERR! stack     import sys; print "%s.%s.%s" % sys.version_info[:3];
gyp ERR! stack                                ^                                                             
gyp ERR! stack SyntaxError: invalid syntax                              
gyp ERR! stack                                            
gyp ERR! stack     at ChildProcess.exithandler (child_process.js:276:12)
gyp ERR! stack     at emitTwo (events.js:126:13)                                                        
gyp ERR! stack     at ChildProcess.emit (events.js:214:7)                            
gyp ERR! stack     at maybeClose (internal/child_process.js:915:16)                                    
gyp ERR! stack     at Socket.stream.socket.on (internal/child_process.js:336:11)                                  
gyp ERR! stack     at emitOne (events.js:116:13)                                                                
gyp ERR! stack     at Socket.emit (events.js:211:7)                                                           
gyp ERR! stack     at Pipe._handle.close [as _onclose] (net.js:561:12)                                        
gyp ERR! System Linux 4.14.87-1-ARCH                                                                   
gyp ERR! command "/home/brandon/.nvm/versions/node/v8.14.0/bin/node" "/home/brandon/.nvm/versions/node/v8.14.0/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
gyp ERR! cwd /home/brandon/repos/esplora/client/node_modules/canvas
gyp ERR! node -v v8.14.0
gyp ERR! node-gyp -v v3.8.0
gyp ERR! not ok
npm WARN esplora-client@0.1.0 No description
npm WARN esplora-client@0.1.0 No repository field.

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! canvas@1.6.13 install: `node-gyp rebuild`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the canvas@1.6.13 install script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/brandon/.npm/_logs/2019-07-04T22_40_54_059Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! esplora@0.1.0 postinstall: `(cd client && npm install) && (cd prerender-server && npm install)`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the esplora@0.1.0 postinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/brandon/.npm/_logs/2019-07-04T22_40_54_373Z-debug.log

Users on systems where python=python3 (e.g. Arch Linux) will have to install python2 (e.g. sudo pacman -S python2) and then alias python to python3 (e.g. alias python=python2) before running npm install.

[omajid]

This is also starting to affect us in Fedora rawhide, where python is python3.

[shesek]

The dependency on the canvas package was removed (it was a sub-dependency of qruri, which was replaced with qrcode in 73cd412 for this exact reason). There should be no other native modules that use node-gyp now, so I believe this should be resolved.

Closing for now, please report back if you're still having issues with the current master.