Stop using node_modules/.bin for Windows compatibility

[tephenavies]

Hopefully fixes error when attempting to run yarn gulp dev on Windows:

basedir=$(dirname "$(echo "$0" | sed -e 's,\\,/,g')")
          ^^^^^^^

SyntaxError: missing ) after argument list
    at Object.compileFunction (node:vm:360:18)
    at wrapSafe (node:internal/modules/cjs/loader:1124:15)
    at Module._compile (node:internal/modules/cjs/loader:1160:27)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1250:10)
    at Module.load (node:internal/modules/cjs/loader:1074:32)
    at Function.Module._load (node:internal/modules/cjs/loader:909:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47

(see TerriaJS/terriajs#6731 (comment))