Update babel-istanbul to 0.8.x

[bmealhouse]

babel-istanbul < 0.8.x cannot handle exporting default anonymous functions (see code example and stack track below). This is due to an issue with escodegen that was fixed and released in babel-istanbul 0.8.0.

I can submit a PR with package.json update if needed.

export default function() {}

/*
Module build failed: TypeError: Cannot read property 'name' of undefined
  at CodeGenerator.Expression.ExportSpecifier (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2265:54)
  at CodeGenerator.generateExpression (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2427:28)
  at /Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:1242:46
  at withIndent (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:582:9)
  at CodeGenerator.Statement.ExportDeclaration (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:1237:21)
  at CodeGenerator.Statement.ExportNamedDeclaration (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:1274:25)
  at CodeGenerator.generateStatement (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2440:33)
  at CodeGenerator.Statement.Program (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:1703:43)
  at CodeGenerator.generateStatement (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2440:33)
  at generateInternal (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2461:28)
  at Object.generate (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/escodegen/escodegen.js:2529:18)
  at Object.Instrumenter.instrumentASTSync (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/babel-istanbul/lib/instrumenter.js:562:32)
  at Object.Instrumenter.instrumentSync (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/babel-istanbul/lib/instrumenter.js:471:25)
  at Object.Instrumenter.instrument (/Users/brent/dev/web/node_modules/babel-istanbul-loader/node_modules/babel-istanbul/lib/instrumenter.js:597:37)
  at Object.module.exports (/Users/brent/dev/web/node_modules/babel-istanbul-loader/index.js:66:18)
*/