DOC: Fix small doc error in EGARCH

Remove absolute values

Author: bashtage

arch/univariate/volatility.py

@@ -1705,7 +1705,7 @@ class EGARCH(VolatilityProcess):
         \ln\sigma_{t}^{2}=\omega
         +\sum_{i=1}^{p}\alpha_{i}
         \left(\left|e_{t-i}\right|-\sqrt{2/\pi}\right)
-        +\sum_{j=1}^{o}\gamma_{j}\left|e_{t-j}\right|
+        +\sum_{j=1}^{o}\gamma_{j} e_{t-j}
         +\sum_{k=1}^{q}\beta_{k}\ln\sigma_{t-k}^{2}
 
     where :math:`e_{t}=\epsilon_{t}/\sigma_{t}`.