Updating SQLAlchemy Dependencies

Ran into an issue this morning attempting to install/bootstrap Mistral...

```
Collecting SQLAlchemy<=0.8.99,<=0.9.99,>=0.8.4,>=0.9.7 (from -r requirements.txt (line 26))
  Could not find a version that satisfies the requirement SQLAlchemy<=0.8.99,<=0.9.99,>=0.8.4,>=0.9.7 (from -r requirements.txt (line 26)) (from versions: 0.4.2p3, 0.4.7p1, 0.5.4p1, 0.5.4p2, 0.1.0, 0.1.1, 0.1.2, 0.1.3, 0.1.4, 0.1.5, 0.1.6, 0.1.7, 0.2.0, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.2.5, 0.2.6, 0.2.7, 0.2.8, 0.3.0, 0
.3.1, 0.3.2, 0.3.3, 0.3.4, 0.3.5, 0.3.6, 0.3.7, 0.3.8, 0.3.9, 0.3.10, 0.3.11, 0.4.0b1, 0.4.0b2, 0.4.0b3, 0.4.0b4, 0.4.0b5, 0.4.0b6, 0.4.0, 0.4.1, 0.4.2a0, 0.4.2b0, 0.4.2, 0.4.3, 0.4.4, 0.4.5, 0.4.6, 0.4.7, 0.4.8, 0.5.0b1, 0.5.0b2, 0.5.0b3, 0.5.0rc1, 0.5.0rc2, 0.5.0rc3, 0.5.0rc4, 0.5.0, 0.5.1, 0.5.2, 0.5.3, 0.5.4, 0.5
.5, 0.5.6, 0.5.7, 0.5.8, 0.6b1, 0.6b2, 0.6b3, 0.6.0, 0.6.1, 0.6.2, 0.6.3, 0.6.4, 0.6.5, 0.6.6, 0.6.7, 0.6.8, 0.6.9, 0.7.0, 0.7.1, 0.7.2, 0.7.3, 0.7.4, 0.7.5, 0.7.6, 0.7.7, 0.7.8, 0.7.9, 0.7.10, 0.8.0b2, 0.8.0, 0.8.1, 0.8.2, 0.8.3, 0.8.4, 0.8.5, 0.8.6, 0.8.7, 0.9.0, 0.9.1, 0.9.2, 0.9.3, 0.9.4, 0.9.5, 0.9.6, 0.9.7, 0.9
.8)
  Some externally hosted files were ignored as access to them may be unreliable (use --allow-external to allow).
  No distributions matching the version for SQLAlchemy<=0.8.99,<=0.9.99,>=0.8.4,>=0.9.7 (from -r requirements.txt (line 26))
```

This change updates the dependency to match upstream `master`, which unblocks an installation.