Update 0136-single-number.md

Author: ajay-dhangar

dsa-solutions/lc-solutions/0100-0199/0136-single-number.md

@@ -40,8 +40,8 @@ Output: 1
 
 ### Constraints
 
-- $1 <= nums.length <= 3 * 10^4$
-- $-3 * 10^4 <= nums[i] <= 3 _ 10^4$
+- $1 \leq nums.length \leq 3 * 10^4$
+- $-3 \times 10^4 \leq nums[i] \leq 3 \times 10^4$
 - Each element in the array appears twice except for one element which appears only once.
 
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