fix compile issue

[ciyengar3]

tried to deploy the v3 subgraph but i ran into a compile issue. Not sure if there is something wrong with my local env tho, but curious to see if others are hitting it

Error: Failed to compile data source mapping: 3 compile error(s)
    at Compiler._compileDataSourceMapping (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/@graphprotocol/graph-cli/dist/compiler/index.js:297:19)
    at /Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/@graphprotocol/graph-cli/dist/compiler/index.js:201:167
    at updateInDeeply (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2121:22)
    at updateInDeeply (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2134:23)
    at updateInDeeply (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2134:23)
    at updateIn$1 (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2099:24)
    at Map.updateIn (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2180:12)
    at /Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/@graphprotocol/graph-cli/dist/compiler/index.js:201:115
    at /Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:3321:30
    at List.withMutations (/Users/crishna.iyengar/Documents/repos/v3-subgraph/node_modules/immutable/dist/immutable.js:2367:5)
UNCAUGHT EXCEPTION: Error: The AssemblyScript compiler crashed when compiling this file: 'src/v3/mappings/factory.ts'
Suggestion: try to comment the whole file and uncomment it little by little while re-running the graph-cli until you isolate the line where the problem happens.
Also, please contact us so we can make the CLI better by handling errors like this. You can reach out in any of these links:
- Discord channel: https://discord.gg/eM8CA6WA9r
- Github issues: https://github.com/graphprotocol/graph-tooling/issues/new/choose